diff --git a/build.gradle b/build.gradle
index ddf10cc8aecb..7b2dd0673418 100644
--- a/build.gradle
+++ b/build.gradle
@@ -81,7 +81,7 @@ buildscript {
     }
 
     dependencies {
-        classpath 'org.mozilla.apilint:apilint:0.1.7'
+        classpath 'org.mozilla.apilint:apilint:0.1.8'
         classpath 'com.android.tools.build:gradle:3.1.4'
         classpath 'com.getkeepsafe.dexcount:dexcount-gradle-plugin:0.8.2'
         classpath 'org.apache.commons:commons-exec:1.3'
diff --git a/mobile/android/geckoview/api.txt b/mobile/android/geckoview/api.txt
index 0ab6825f5c8e..6b8d1f4924d3 100644
--- a/mobile/android/geckoview/api.txt
+++ b/mobile/android/geckoview/api.txt
@@ -71,7 +71,7 @@ package org.mozilla.geckoview {
   }
 
   public static interface ContentBlocking.Delegate {
-    method @android.support.annotation.UiThread public void onContentBlocked(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull org.mozilla.geckoview.ContentBlocking.BlockEvent);
+    method @android.support.annotation.UiThread default public void onContentBlocked(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull org.mozilla.geckoview.ContentBlocking.BlockEvent);
   }
 
   @android.support.annotation.AnyThread public static class ContentBlocking.Settings extends org.mozilla.geckoview.RuntimeSettings {
@@ -124,9 +124,9 @@ package org.mozilla.geckoview {
   }
 
   public static interface DynamicToolbarAnimator.ToolbarChromeProxy {
-    method @android.support.annotation.UiThread @android.support.annotation.Nullable public android.graphics.Bitmap getBitmapOfToolbarChrome();
-    method @android.support.annotation.UiThread public boolean isToolbarChromeVisible();
-    method @android.support.annotation.UiThread public void toggleToolbarChrome(boolean);
+    method @android.support.annotation.UiThread @android.support.annotation.Nullable default public android.graphics.Bitmap getBitmapOfToolbarChrome();
+    method @android.support.annotation.UiThread default public boolean isToolbarChromeVisible();
+    method @android.support.annotation.UiThread default public void toggleToolbarChrome(boolean);
   }
 
   public class GeckoDisplay {
@@ -345,14 +345,14 @@ package org.mozilla.geckoview {
   }
 
   public static interface GeckoSession.ContentDelegate {
-    method @android.support.annotation.UiThread public void onCloseRequest(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession);
-    method @android.support.annotation.UiThread public void onContextMenu(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, int, int, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.ContentDelegate.ContextElement);
-    method @android.support.annotation.UiThread public void onCrash(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession);
-    method @android.support.annotation.UiThread public void onExternalResponse(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.WebResponseInfo);
-    method @android.support.annotation.UiThread public void onFirstComposite(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession);
-    method @android.support.annotation.UiThread public void onFocusRequest(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession);
-    method @android.support.annotation.UiThread public void onFullScreen(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, boolean);
-    method @android.support.annotation.UiThread public void onTitleChange(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String);
+    method @android.support.annotation.UiThread default public void onCloseRequest(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession);
+    method @android.support.annotation.UiThread default public void onContextMenu(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, int, int, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.ContentDelegate.ContextElement);
+    method @android.support.annotation.UiThread default public void onCrash(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession);
+    method @android.support.annotation.UiThread default public void onExternalResponse(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.WebResponseInfo);
+    method @android.support.annotation.UiThread default public void onFirstComposite(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession);
+    method @android.support.annotation.UiThread default public void onFocusRequest(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession);
+    method @android.support.annotation.UiThread default public void onFullScreen(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, boolean);
+    method @android.support.annotation.UiThread default public void onTitleChange(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String);
   }
 
   public static class GeckoSession.ContentDelegate.ContextElement {
@@ -382,8 +382,8 @@ package org.mozilla.geckoview {
   }
 
   public static interface GeckoSession.HistoryDelegate {
-    method @android.support.annotation.UiThread @android.support.annotation.Nullable public org.mozilla.geckoview.GeckoResult<boolean[]> getVisited(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull java.lang.String[]);
-    method @android.support.annotation.UiThread @android.support.annotation.Nullable public org.mozilla.geckoview.GeckoResult<java.lang.Boolean> onVisited(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull java.lang.String, @android.support.annotation.Nullable java.lang.String, int);
+    method @android.support.annotation.UiThread @android.support.annotation.Nullable default public org.mozilla.geckoview.GeckoResult<boolean[]> getVisited(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull java.lang.String[]);
+    method @android.support.annotation.UiThread @android.support.annotation.Nullable default public org.mozilla.geckoview.GeckoResult<java.lang.Boolean> onVisited(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull java.lang.String, @android.support.annotation.Nullable java.lang.String, int);
     field public static final int VISIT_REDIRECT_PERMANENT = 4;
     field public static final int VISIT_REDIRECT_SOURCE = 8;
     field public static final int VISIT_REDIRECT_SOURCE_PERMANENT = 16;
@@ -396,17 +396,17 @@ package org.mozilla.geckoview {
   }
 
   public static interface GeckoSession.MediaDelegate {
-    method @android.support.annotation.UiThread public void onMediaAdd(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull org.mozilla.geckoview.MediaElement);
-    method @android.support.annotation.UiThread public void onMediaRemove(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull org.mozilla.geckoview.MediaElement);
+    method @android.support.annotation.UiThread default public void onMediaAdd(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull org.mozilla.geckoview.MediaElement);
+    method @android.support.annotation.UiThread default public void onMediaRemove(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull org.mozilla.geckoview.MediaElement);
   }
 
   public static interface GeckoSession.NavigationDelegate {
-    method @android.support.annotation.UiThread public void onCanGoBack(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, boolean);
-    method @android.support.annotation.UiThread public void onCanGoForward(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, boolean);
-    method @android.support.annotation.UiThread @android.support.annotation.Nullable public org.mozilla.geckoview.GeckoResult<java.lang.String> onLoadError(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.NonNull org.mozilla.geckoview.WebRequestError);
-    method @android.support.annotation.UiThread @android.support.annotation.Nullable public org.mozilla.geckoview.GeckoResult<org.mozilla.geckoview.AllowOrDeny> onLoadRequest(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.NavigationDelegate.LoadRequest);
-    method @android.support.annotation.UiThread public void onLocationChange(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String);
-    method @android.support.annotation.UiThread @android.support.annotation.Nullable public org.mozilla.geckoview.GeckoResult<org.mozilla.geckoview.GeckoSession> onNewSession(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull java.lang.String);
+    method @android.support.annotation.UiThread default public void onCanGoBack(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, boolean);
+    method @android.support.annotation.UiThread default public void onCanGoForward(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, boolean);
+    method @android.support.annotation.UiThread @android.support.annotation.Nullable default public org.mozilla.geckoview.GeckoResult<java.lang.String> onLoadError(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.NonNull org.mozilla.geckoview.WebRequestError);
+    method @android.support.annotation.UiThread @android.support.annotation.Nullable default public org.mozilla.geckoview.GeckoResult<org.mozilla.geckoview.AllowOrDeny> onLoadRequest(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.NavigationDelegate.LoadRequest);
+    method @android.support.annotation.UiThread default public void onLocationChange(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String);
+    method @android.support.annotation.UiThread @android.support.annotation.Nullable default public org.mozilla.geckoview.GeckoResult<org.mozilla.geckoview.GeckoSession> onNewSession(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull java.lang.String);
     field public static final int LOAD_REQUEST_IS_REDIRECT = 8388608;
     field public static final int TARGET_WINDOW_CURRENT = 1;
     field public static final int TARGET_WINDOW_NEW = 2;
@@ -425,22 +425,22 @@ package org.mozilla.geckoview {
   }
 
   public static interface GeckoSession.PermissionDelegate {
-    method @android.support.annotation.UiThread public void onAndroidPermissionsRequest(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String[], @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PermissionDelegate.Callback);
-    method @android.support.annotation.UiThread public void onContentPermissionRequest(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String, int, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PermissionDelegate.Callback);
-    method @android.support.annotation.UiThread public void onMediaPermissionRequest(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull java.lang.String, @android.support.annotation.Nullable org.mozilla.geckoview.GeckoSession.PermissionDelegate.MediaSource[], @android.support.annotation.Nullable org.mozilla.geckoview.GeckoSession.PermissionDelegate.MediaSource[], @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PermissionDelegate.MediaCallback);
+    method @android.support.annotation.UiThread default public void onAndroidPermissionsRequest(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String[], @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PermissionDelegate.Callback);
+    method @android.support.annotation.UiThread default public void onContentPermissionRequest(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String, int, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PermissionDelegate.Callback);
+    method @android.support.annotation.UiThread default public void onMediaPermissionRequest(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull java.lang.String, @android.support.annotation.Nullable org.mozilla.geckoview.GeckoSession.PermissionDelegate.MediaSource[], @android.support.annotation.Nullable org.mozilla.geckoview.GeckoSession.PermissionDelegate.MediaSource[], @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PermissionDelegate.MediaCallback);
     field public static final int PERMISSION_DESKTOP_NOTIFICATION = 1;
     field public static final int PERMISSION_GEOLOCATION = 0;
   }
 
   public static interface GeckoSession.PermissionDelegate.Callback {
-    method @android.support.annotation.UiThread public void grant();
-    method @android.support.annotation.UiThread public void reject();
+    method @android.support.annotation.UiThread default public void grant();
+    method @android.support.annotation.UiThread default public void reject();
   }
 
   public static interface GeckoSession.PermissionDelegate.MediaCallback {
-    method @android.support.annotation.UiThread public void grant(@android.support.annotation.Nullable java.lang.String, @android.support.annotation.Nullable java.lang.String);
-    method @android.support.annotation.UiThread public void grant(@android.support.annotation.Nullable org.mozilla.geckoview.GeckoSession.PermissionDelegate.MediaSource, @android.support.annotation.Nullable org.mozilla.geckoview.GeckoSession.PermissionDelegate.MediaSource);
-    method @android.support.annotation.UiThread public void reject();
+    method @android.support.annotation.UiThread default public void grant(@android.support.annotation.Nullable java.lang.String, @android.support.annotation.Nullable java.lang.String);
+    method @android.support.annotation.UiThread default public void grant(@android.support.annotation.Nullable org.mozilla.geckoview.GeckoSession.PermissionDelegate.MediaSource, @android.support.annotation.Nullable org.mozilla.geckoview.GeckoSession.PermissionDelegate.MediaSource);
+    method @android.support.annotation.UiThread default public void reject();
   }
 
   public static class GeckoSession.PermissionDelegate.MediaSource {
@@ -466,10 +466,10 @@ package org.mozilla.geckoview {
   }
 
   public static interface GeckoSession.ProgressDelegate {
-    method @android.support.annotation.UiThread public void onPageStart(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull java.lang.String);
-    method @android.support.annotation.UiThread public void onPageStop(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, boolean);
-    method @android.support.annotation.UiThread public void onProgressChange(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, int);
-    method @android.support.annotation.UiThread public void onSecurityChange(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.ProgressDelegate.SecurityInformation);
+    method @android.support.annotation.UiThread default public void onPageStart(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull java.lang.String);
+    method @android.support.annotation.UiThread default public void onPageStop(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, boolean);
+    method @android.support.annotation.UiThread default public void onProgressChange(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, int);
+    method @android.support.annotation.UiThread default public void onSecurityChange(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.ProgressDelegate.SecurityInformation);
   }
 
   public static class GeckoSession.ProgressDelegate.SecurityInformation {
@@ -494,15 +494,15 @@ package org.mozilla.geckoview {
   }
 
   public static interface GeckoSession.PromptDelegate {
-    method @android.support.annotation.UiThread public void onAlert(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PromptDelegate.AlertCallback);
-    method @android.support.annotation.UiThread public void onAuthPrompt(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PromptDelegate.AuthOptions, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PromptDelegate.AuthCallback);
-    method @android.support.annotation.UiThread public void onButtonPrompt(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.Nullable java.lang.String[], @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PromptDelegate.ButtonCallback);
-    method @android.support.annotation.UiThread public void onChoicePrompt(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.Nullable java.lang.String, int, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PromptDelegate.Choice[], @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PromptDelegate.ChoiceCallback);
-    method @android.support.annotation.UiThread public void onColorPrompt(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PromptDelegate.TextCallback);
-    method @android.support.annotation.UiThread public void onDateTimePrompt(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String, int, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PromptDelegate.TextCallback);
-    method @android.support.annotation.UiThread public void onFilePrompt(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String, int, @android.support.annotation.Nullable java.lang.String[], @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PromptDelegate.FileCallback);
-    method @android.support.annotation.UiThread @android.support.annotation.Nullable public org.mozilla.geckoview.GeckoResult<org.mozilla.geckoview.AllowOrDeny> onPopupRequest(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String);
-    method @android.support.annotation.UiThread public void onTextPrompt(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PromptDelegate.TextCallback);
+    method @android.support.annotation.UiThread default public void onAlert(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PromptDelegate.AlertCallback);
+    method @android.support.annotation.UiThread default public void onAuthPrompt(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PromptDelegate.AuthOptions, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PromptDelegate.AuthCallback);
+    method @android.support.annotation.UiThread default public void onButtonPrompt(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.Nullable java.lang.String[], @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PromptDelegate.ButtonCallback);
+    method @android.support.annotation.UiThread default public void onChoicePrompt(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.Nullable java.lang.String, int, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PromptDelegate.Choice[], @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PromptDelegate.ChoiceCallback);
+    method @android.support.annotation.UiThread default public void onColorPrompt(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PromptDelegate.TextCallback);
+    method @android.support.annotation.UiThread default public void onDateTimePrompt(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String, int, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PromptDelegate.TextCallback);
+    method @android.support.annotation.UiThread default public void onFilePrompt(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String, int, @android.support.annotation.Nullable java.lang.String[], @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PromptDelegate.FileCallback);
+    method @android.support.annotation.UiThread @android.support.annotation.Nullable default public org.mozilla.geckoview.GeckoResult<org.mozilla.geckoview.AllowOrDeny> onPopupRequest(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String);
+    method @android.support.annotation.UiThread default public void onTextPrompt(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.Nullable java.lang.String, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PromptDelegate.TextCallback);
     field public static final int BUTTON_TYPE_NEGATIVE = 2;
     field public static final int BUTTON_TYPE_NEUTRAL = 1;
     field public static final int BUTTON_TYPE_POSITIVE = 0;
@@ -516,16 +516,16 @@ package org.mozilla.geckoview {
   }
 
   public static interface GeckoSession.PromptDelegate.AlertCallback {
-    method @android.support.annotation.UiThread public void dismiss();
-    method @android.support.annotation.UiThread @android.support.annotation.Nullable public java.lang.String getCheckboxMessage();
-    method @android.support.annotation.UiThread public boolean getCheckboxValue();
-    method @android.support.annotation.UiThread public boolean hasCheckbox();
-    method @android.support.annotation.UiThread public void setCheckboxValue(boolean);
+    method @android.support.annotation.UiThread default public void dismiss();
+    method @android.support.annotation.UiThread @android.support.annotation.Nullable default public java.lang.String getCheckboxMessage();
+    method @android.support.annotation.UiThread default public boolean getCheckboxValue();
+    method @android.support.annotation.UiThread default public boolean hasCheckbox();
+    method @android.support.annotation.UiThread default public void setCheckboxValue(boolean);
   }
 
   public static interface GeckoSession.PromptDelegate.AuthCallback implements org.mozilla.geckoview.GeckoSession.PromptDelegate.AlertCallback {
-    method @android.support.annotation.UiThread public void confirm(@android.support.annotation.Nullable java.lang.String);
-    method @android.support.annotation.UiThread public void confirm(@android.support.annotation.NonNull java.lang.String, @android.support.annotation.NonNull java.lang.String);
+    method @android.support.annotation.UiThread default public void confirm(@android.support.annotation.Nullable java.lang.String);
+    method @android.support.annotation.UiThread default public void confirm(@android.support.annotation.NonNull java.lang.String, @android.support.annotation.NonNull java.lang.String);
   }
 
   public static class GeckoSession.PromptDelegate.AuthOptions {
@@ -546,7 +546,7 @@ package org.mozilla.geckoview {
   }
 
   public static interface GeckoSession.PromptDelegate.ButtonCallback implements org.mozilla.geckoview.GeckoSession.PromptDelegate.AlertCallback {
-    method @android.support.annotation.UiThread public void confirm(int);
+    method @android.support.annotation.UiThread default public void confirm(int);
   }
 
   public static class GeckoSession.PromptDelegate.Choice {
@@ -564,34 +564,34 @@ package org.mozilla.geckoview {
   }
 
   public static interface GeckoSession.PromptDelegate.ChoiceCallback implements org.mozilla.geckoview.GeckoSession.PromptDelegate.AlertCallback {
-    method @android.support.annotation.UiThread public void confirm(@android.support.annotation.Nullable java.lang.String);
-    method @android.support.annotation.UiThread public void confirm(@android.support.annotation.NonNull java.lang.String[]);
-    method @android.support.annotation.UiThread public void confirm(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PromptDelegate.Choice);
-    method @android.support.annotation.UiThread public void confirm(@android.support.annotation.Nullable org.mozilla.geckoview.GeckoSession.PromptDelegate.Choice[]);
+    method @android.support.annotation.UiThread default public void confirm(@android.support.annotation.Nullable java.lang.String);
+    method @android.support.annotation.UiThread default public void confirm(@android.support.annotation.NonNull java.lang.String[]);
+    method @android.support.annotation.UiThread default public void confirm(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.PromptDelegate.Choice);
+    method @android.support.annotation.UiThread default public void confirm(@android.support.annotation.Nullable org.mozilla.geckoview.GeckoSession.PromptDelegate.Choice[]);
   }
 
   public static interface GeckoSession.PromptDelegate.DatetimeType implements java.lang.annotation.Annotation {
   }
 
   public static interface GeckoSession.PromptDelegate.FileCallback implements org.mozilla.geckoview.GeckoSession.PromptDelegate.AlertCallback {
-    method @android.support.annotation.UiThread public void confirm(@android.support.annotation.Nullable android.content.Context, @android.support.annotation.Nullable android.net.Uri);
-    method @android.support.annotation.UiThread public void confirm(@android.support.annotation.Nullable android.content.Context, @android.support.annotation.Nullable android.net.Uri[]);
+    method @android.support.annotation.UiThread default public void confirm(@android.support.annotation.Nullable android.content.Context, @android.support.annotation.Nullable android.net.Uri);
+    method @android.support.annotation.UiThread default public void confirm(@android.support.annotation.Nullable android.content.Context, @android.support.annotation.Nullable android.net.Uri[]);
   }
 
   public static interface GeckoSession.PromptDelegate.FileType implements java.lang.annotation.Annotation {
   }
 
   public static interface GeckoSession.PromptDelegate.TextCallback implements org.mozilla.geckoview.GeckoSession.PromptDelegate.AlertCallback {
-    method @android.support.annotation.UiThread public void confirm(@android.support.annotation.Nullable java.lang.String);
+    method @android.support.annotation.UiThread default public void confirm(@android.support.annotation.Nullable java.lang.String);
   }
 
   public static interface GeckoSession.ScrollDelegate {
-    method @android.support.annotation.UiThread public void onScrollChanged(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, int, int);
+    method @android.support.annotation.UiThread default public void onScrollChanged(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, int, int);
   }
 
   public static interface GeckoSession.SelectionActionDelegate {
-    method @android.support.annotation.UiThread public void onHideAction(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, int);
-    method @android.support.annotation.UiThread public void onShowActionRequest(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.SelectionActionDelegate.Selection, java.lang.String[], @android.support.annotation.NonNull org.mozilla.geckoview.GeckoResponse<java.lang.String>);
+    method @android.support.annotation.UiThread default public void onHideAction(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, int);
+    method @android.support.annotation.UiThread default public void onShowActionRequest(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession.SelectionActionDelegate.Selection, java.lang.String[], @android.support.annotation.NonNull org.mozilla.geckoview.GeckoResponse<java.lang.String>);
     field public static final java.lang.String ACTION_COLLAPSE_TO_END = "org.mozilla.geckoview.COLLAPSE_TO_END";
     field public static final java.lang.String ACTION_COLLAPSE_TO_START = "org.mozilla.geckoview.COLLAPSE_TO_START";
     field public static final java.lang.String ACTION_COPY = "org.mozilla.geckoview.COPY";
@@ -633,13 +633,13 @@ package org.mozilla.geckoview {
   }
 
   public static interface GeckoSession.TextInputDelegate {
-    method @android.support.annotation.UiThread public void hideSoftInput(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession);
-    method @android.support.annotation.UiThread public void notifyAutoFill(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, int, int);
-    method @android.support.annotation.UiThread public void restartInput(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, int);
-    method @android.support.annotation.UiThread public void showSoftInput(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession);
-    method @android.support.annotation.UiThread public void updateCursorAnchorInfo(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull android.view.inputmethod.CursorAnchorInfo);
-    method @android.support.annotation.UiThread public void updateExtractedText(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull android.view.inputmethod.ExtractedTextRequest, @android.support.annotation.NonNull android.view.inputmethod.ExtractedText);
-    method @android.support.annotation.UiThread public void updateSelection(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, int, int, int, int);
+    method @android.support.annotation.UiThread default public void hideSoftInput(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession);
+    method @android.support.annotation.UiThread default public void notifyAutoFill(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, int, int);
+    method @android.support.annotation.UiThread default public void restartInput(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, int);
+    method @android.support.annotation.UiThread default public void showSoftInput(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession);
+    method @android.support.annotation.UiThread default public void updateCursorAnchorInfo(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull android.view.inputmethod.CursorAnchorInfo);
+    method @android.support.annotation.UiThread default public void updateExtractedText(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, @android.support.annotation.NonNull android.view.inputmethod.ExtractedTextRequest, @android.support.annotation.NonNull android.view.inputmethod.ExtractedText);
+    method @android.support.annotation.UiThread default public void updateSelection(@android.support.annotation.NonNull org.mozilla.geckoview.GeckoSession, int, int, int, int);
     field public static final int AUTO_FILL_NOTIFY_CANCELED = 2;
     field public static final int AUTO_FILL_NOTIFY_COMMITTED = 1;
     field public static final int AUTO_FILL_NOTIFY_STARTED = 0;
@@ -797,15 +797,15 @@ package org.mozilla.geckoview {
   }
 
   public static interface MediaElement.Delegate {
-    method @android.support.annotation.UiThread public void onError(@android.support.annotation.NonNull org.mozilla.geckoview.MediaElement, int);
-    method @android.support.annotation.UiThread public void onFullscreenChange(@android.support.annotation.NonNull org.mozilla.geckoview.MediaElement, boolean);
-    method @android.support.annotation.UiThread public void onLoadProgress(@android.support.annotation.NonNull org.mozilla.geckoview.MediaElement, @android.support.annotation.NonNull org.mozilla.geckoview.MediaElement.LoadProgressInfo);
-    method @android.support.annotation.UiThread public void onMetadataChange(@android.support.annotation.NonNull org.mozilla.geckoview.MediaElement, @android.support.annotation.NonNull org.mozilla.geckoview.MediaElement.Metadata);
-    method @android.support.annotation.UiThread public void onPlaybackRateChange(@android.support.annotation.NonNull org.mozilla.geckoview.MediaElement, double);
-    method @android.support.annotation.UiThread public void onPlaybackStateChange(@android.support.annotation.NonNull org.mozilla.geckoview.MediaElement, int);
-    method @android.support.annotation.UiThread public void onReadyStateChange(@android.support.annotation.NonNull org.mozilla.geckoview.MediaElement, int);
-    method @android.support.annotation.UiThread public void onTimeChange(@android.support.annotation.NonNull org.mozilla.geckoview.MediaElement, double);
-    method @android.support.annotation.UiThread public void onVolumeChange(@android.support.annotation.NonNull org.mozilla.geckoview.MediaElement, double, boolean);
+    method @android.support.annotation.UiThread default public void onError(@android.support.annotation.NonNull org.mozilla.geckoview.MediaElement, int);
+    method @android.support.annotation.UiThread default public void onFullscreenChange(@android.support.annotation.NonNull org.mozilla.geckoview.MediaElement, boolean);
+    method @android.support.annotation.UiThread default public void onLoadProgress(@android.support.annotation.NonNull org.mozilla.geckoview.MediaElement, @android.support.annotation.NonNull org.mozilla.geckoview.MediaElement.LoadProgressInfo);
+    method @android.support.annotation.UiThread default public void onMetadataChange(@android.support.annotation.NonNull org.mozilla.geckoview.MediaElement, @android.support.annotation.NonNull org.mozilla.geckoview.MediaElement.Metadata);
+    method @android.support.annotation.UiThread default public void onPlaybackRateChange(@android.support.annotation.NonNull org.mozilla.geckoview.MediaElement, double);
+    method @android.support.annotation.UiThread default public void onPlaybackStateChange(@android.support.annotation.NonNull org.mozilla.geckoview.MediaElement, int);
+    method @android.support.annotation.UiThread default public void onReadyStateChange(@android.support.annotation.NonNull org.mozilla.geckoview.MediaElement, int);
+    method @android.support.annotation.UiThread default public void onTimeChange(@android.support.annotation.NonNull org.mozilla.geckoview.MediaElement, double);
+    method @android.support.annotation.UiThread default public void onVolumeChange(@android.support.annotation.NonNull org.mozilla.geckoview.MediaElement, double, boolean);
   }
 
   public static class MediaElement.LoadProgressInfo {
diff --git a/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/DynamicToolbarAnimator.java b/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/DynamicToolbarAnimator.java
index e38dc1779ae1..907175ef7f2f 100644
--- a/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/DynamicToolbarAnimator.java
+++ b/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/DynamicToolbarAnimator.java
@@ -40,11 +40,15 @@ public final class DynamicToolbarAnimator {
 
     public interface ToolbarChromeProxy {
         @UiThread
-        public @Nullable Bitmap getBitmapOfToolbarChrome();
+        @Nullable default Bitmap getBitmapOfToolbarChrome() {
+            return null;
+        }
         @UiThread
-        public boolean isToolbarChromeVisible();
+        default boolean isToolbarChromeVisible() {
+            return false;
+        }
         @UiThread
-        public void toggleToolbarChrome(boolean aShow);
+        default void toggleToolbarChrome(boolean aShow) {}
     }
 
     private final Set<PinReason> mPinFlags = EnumSet.noneOf(PinReason.class);
diff --git a/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/GeckoSession.java b/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/GeckoSession.java
index 27b908505b56..5719d13a1a5e 100644
--- a/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/GeckoSession.java
+++ b/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/GeckoSession.java
@@ -3123,7 +3123,7 @@ public class GeckoSession implements Parcelable {
              * must call dismiss() or confirm(), if available, when the prompt is dismissed.
              */
             @UiThread
-            void dismiss();
+            default void dismiss() {}
 
             /**
              * Return whether the prompt shown should include a checkbox. For example, if
@@ -3135,7 +3135,9 @@ public class GeckoSession implements Parcelable {
              * @return True if prompt includes a checkbox.
              */
             @UiThread
-            boolean hasCheckbox();
+            default boolean hasCheckbox() {
+                return false;
+            }
 
             /**
              * Return the message label for the optional checkbox.
@@ -3143,7 +3145,9 @@ public class GeckoSession implements Parcelable {
              * @return Checkbox message or null if none.
              */
             @UiThread
-            @Nullable String getCheckboxMessage();
+            @Nullable default String getCheckboxMessage() {
+                return null;
+            }
 
             /**
              * Return the initial value for the optional checkbox.
@@ -3151,7 +3155,9 @@ public class GeckoSession implements Parcelable {
              * @return Initial checkbox value.
              */
             @UiThread
-            boolean getCheckboxValue();
+            default boolean getCheckboxValue() {
+                return false;
+            }
 
             /**
              * Set the current value for the optional checkbox.
@@ -3159,7 +3165,7 @@ public class GeckoSession implements Parcelable {
              * @param value New checkbox value.
              */
             @UiThread
-            void setCheckboxValue(boolean value);
+            default void setCheckboxValue(boolean value) {}
         }
 
         /**
@@ -3188,7 +3194,7 @@ public class GeckoSession implements Parcelable {
              * @param button Button result; one of BUTTON_TYPE_* constants.
              */
             @UiThread
-            void confirm(int button);
+            default void confirm(int button) {}
         }
 
         static final int BUTTON_TYPE_POSITIVE = 0;
@@ -3228,7 +3234,7 @@ public class GeckoSession implements Parcelable {
              * @param text Text result.
              */
             @UiThread
-            void confirm(@Nullable String text);
+            default void confirm(@Nullable String text) {}
         }
 
         /**
@@ -3259,7 +3265,7 @@ public class GeckoSession implements Parcelable {
              * @param password Entered password.
              */
             @UiThread
-            void confirm(@Nullable String password);
+            default void confirm(@Nullable String password) {}
 
             /**
              * Called by the prompt implementation when a username/password prompt is
@@ -3269,7 +3275,7 @@ public class GeckoSession implements Parcelable {
              * @param password Entered password.
              */
             @UiThread
-            void confirm(@NonNull String username, @NonNull String password);
+            default void confirm(@NonNull String username, @NonNull String password) {}
         }
 
         class AuthOptions {
@@ -3483,7 +3489,7 @@ public class GeckoSession implements Parcelable {
              * @param id ID of the selected item.
              */
             @UiThread
-            void confirm(@Nullable String id);
+            default void confirm(@Nullable String id) {}
 
             /**
              * Called by the prompt implementation when the multiple-choice list is
@@ -3492,7 +3498,7 @@ public class GeckoSession implements Parcelable {
              * @param ids IDs of the selected items.
              */
             @UiThread
-            void confirm(@NonNull String[] ids);
+            default void confirm(@NonNull String[] ids) {}
 
             /**
              * Called by the prompt implementation when the menu or single-choice list is
@@ -3502,7 +3508,7 @@ public class GeckoSession implements Parcelable {
              *             Choice object that was passed to the implementation.
              */
             @UiThread
-            void confirm(@NonNull Choice item);
+            default void confirm(@NonNull Choice item) {}
 
             /**
              * Called by the prompt implementation when the multiple-choice list is
@@ -3512,7 +3518,7 @@ public class GeckoSession implements Parcelable {
              *              Choice objects that were passed to the implementation.
              */
             @UiThread
-            void confirm(@Nullable Choice[] items);
+            default void confirm(@Nullable Choice[] items) {}
         }
 
 
@@ -3612,7 +3618,7 @@ public class GeckoSession implements Parcelable {
              * @param uri The URI of the selected file.
              */
             @UiThread
-            void confirm(@Nullable Context context, @Nullable Uri uri);
+            default void confirm(@Nullable Context context, @Nullable Uri uri) {}
 
             /**
              * Called by the prompt implementation when the user makes file selections in
@@ -3622,7 +3628,7 @@ public class GeckoSession implements Parcelable {
              * @param uris Array of URI objects for the selected files.
              */
             @UiThread
-            void confirm(@Nullable Context context, @Nullable Uri[] uris);
+            default void confirm(@Nullable Context context, @Nullable Uri[] uris) {}
         }
 
         @Retention(RetentionPolicy.SOURCE)
@@ -3882,14 +3888,14 @@ public class GeckoSession implements Parcelable {
              * implementation must call either grant() or reject() for every request.
              */
             @UiThread
-            void grant();
+            default void grant() {}
 
             /**
              * Called by the implementation when permissions are not granted; the
              * implementation must call either grant() or reject() for every request.
              */
             @UiThread
-            void reject();
+            default void reject() {}
         }
 
         /**
@@ -4089,7 +4095,7 @@ public class GeckoSession implements Parcelable {
              *              or null when audio is not requested.
              */
             @UiThread
-            void grant(final @Nullable String video, final @Nullable String audio);
+            default void grant(final @Nullable String video, final @Nullable String audio) {}
 
             /**
              * Called by the implementation after permissions are granted; the
@@ -4103,14 +4109,14 @@ public class GeckoSession implements Parcelable {
              *              or null when audio is not requested.
              */
             @UiThread
-            void grant(final @Nullable MediaSource video, final @Nullable MediaSource audio);
+            default void grant(final @Nullable MediaSource video, final @Nullable MediaSource audio) {}
 
             /**
              * Called by the implementation when permissions are not granted; the
              * implementation must call one of grant() or reject() for every request.
              */
             @UiThread
-            void reject();
+            default void reject() {}
         }
 
         /**
@@ -4172,7 +4178,7 @@ public class GeckoSession implements Parcelable {
          * @param reason Reason for the reset.
          */
         @UiThread
-        void restartInput(@NonNull GeckoSession session, @RestartReason int reason);
+        default void restartInput(@NonNull GeckoSession session, @RestartReason int reason) {}
 
         /**
          * Display the soft input. May be called consecutively, even if the soft input is
@@ -4182,7 +4188,7 @@ public class GeckoSession implements Parcelable {
          * @see #hideSoftInput
          * */
         @UiThread
-        void showSoftInput(@NonNull GeckoSession session);
+        default void showSoftInput(@NonNull GeckoSession session) {}
 
         /**
          * Hide the soft input. May be called consecutively, even if the soft input is
@@ -4192,7 +4198,7 @@ public class GeckoSession implements Parcelable {
          * @see #showSoftInput
          * */
         @UiThread
-        void hideSoftInput(@NonNull GeckoSession session);
+        default void hideSoftInput(@NonNull GeckoSession session) {}
 
         /**
          * Update the soft input on the current selection. This method is <i>not</i> called
@@ -4205,8 +4211,8 @@ public class GeckoSession implements Parcelable {
          * @param compositionEnd Composition end offset, or -1 if there is no composition.
          */
         @UiThread
-        void updateSelection(@NonNull GeckoSession session, int selStart, int selEnd,
-                             int compositionStart, int compositionEnd);
+        default void updateSelection(@NonNull GeckoSession session, int selStart, int selEnd,
+                                     int compositionStart, int compositionEnd) {}
 
         /**
          * Update the soft input on the current extracted text, as requested through
@@ -4218,9 +4224,9 @@ public class GeckoSession implements Parcelable {
          * @param text The extracted text.
          */
         @UiThread
-        void updateExtractedText(@NonNull GeckoSession session,
-                                 @NonNull ExtractedTextRequest request,
-                                 @NonNull ExtractedText text);
+        default void updateExtractedText(@NonNull GeckoSession session,
+                                         @NonNull ExtractedTextRequest request,
+                                         @NonNull ExtractedText text) {}
 
         /**
          * Update the cursor-anchor information as requested through
@@ -4231,7 +4237,8 @@ public class GeckoSession implements Parcelable {
          * @param info Cursor-anchor information.
          */
         @UiThread
-        void updateCursorAnchorInfo(@NonNull GeckoSession session, @NonNull CursorAnchorInfo info);
+        default void updateCursorAnchorInfo(@NonNull GeckoSession session,
+                                            @NonNull CursorAnchorInfo info) {}
 
         @Retention(RetentionPolicy.SOURCE)
         @IntDef({AUTO_FILL_NOTIFY_STARTED, AUTO_FILL_NOTIFY_COMMITTED, AUTO_FILL_NOTIFY_CANCELED,
@@ -4271,8 +4278,9 @@ public class GeckoSession implements Parcelable {
          *                  with {@link SessionTextInput#autofill}.
          */
         @UiThread
-        void notifyAutoFill(@NonNull GeckoSession session, @AutoFillNotification int notification,
-                            int virtualId);
+        default void notifyAutoFill(@NonNull GeckoSession session,
+                                    @AutoFillNotification int notification,
+                                    int virtualId) {}
     }
 
     /* package */ void onSurfaceChanged(final Surface surface, final int x, final int y, final int width,
diff --git a/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/MediaElement.java b/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/MediaElement.java
index 73f3b3173545..35b159afd612 100644
--- a/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/MediaElement.java
+++ b/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/MediaElement.java
@@ -292,7 +292,8 @@ public class MediaElement {
          *                   One of the {@link #MEDIA_STATE_PLAY MEDIA_STATE_*} flags.
          */
         @UiThread
-        void onPlaybackStateChange(@NonNull MediaElement mediaElement, @MediaStateFlags int mediaState);
+        default void onPlaybackStateChange(@NonNull MediaElement mediaElement,
+                                           @MediaStateFlags int mediaState) {}
 
         /**
          * The readiness state of the media has changed.
@@ -302,7 +303,8 @@ public class MediaElement {
          *                   One of the {@link #MEDIA_READY_STATE_HAVE_NOTHING MEDIA_READY_STATE_*} flags.
          */
         @UiThread
-        void onReadyStateChange(@NonNull MediaElement mediaElement, @ReadyStateFlags int readyState);
+        default void onReadyStateChange(@NonNull MediaElement mediaElement,
+                                        @ReadyStateFlags int readyState) {}
 
         /**
          * The media metadata has loaded or changed.
@@ -311,7 +313,8 @@ public class MediaElement {
          * @param metaData The MetaData values of the media.
          */
         @UiThread
-        void onMetadataChange(@NonNull MediaElement mediaElement, @NonNull Metadata metaData);
+        default void onMetadataChange(@NonNull MediaElement mediaElement,
+                                      @NonNull Metadata metaData) {}
 
         /**
          * Indicates that a loading operation is in progress for the media.
@@ -320,8 +323,8 @@ public class MediaElement {
          * @param progressInfo Information about the load progress and buffered ranges.
          */
         @UiThread
-        void onLoadProgress(@NonNull MediaElement mediaElement,
-                            @NonNull LoadProgressInfo progressInfo);
+        default void onLoadProgress(@NonNull MediaElement mediaElement,
+                                    @NonNull LoadProgressInfo progressInfo) {}
 
         /**
          * The media audio volume has changed.
@@ -331,7 +334,8 @@ public class MediaElement {
          * @param muted True if the media is muted.
          */
         @UiThread
-        void onVolumeChange(@NonNull MediaElement mediaElement, double volume, boolean muted);
+        default void onVolumeChange(@NonNull MediaElement mediaElement, double volume,
+                                    boolean muted) {}
 
         /**
          * The current playback time has changed. This event is usually dispatched every 250ms.
@@ -340,7 +344,7 @@ public class MediaElement {
          * @param time The current playback time in seconds.
          */
         @UiThread
-        void onTimeChange(@NonNull MediaElement mediaElement, double time);
+        default void onTimeChange(@NonNull MediaElement mediaElement, double time) {}
 
         /**
          * The media playback speed has changed.
@@ -349,7 +353,7 @@ public class MediaElement {
          * @param rate The current playback rate. A value of 1.0 indicates normal speed.
          */
         @UiThread
-        void onPlaybackRateChange(@NonNull MediaElement mediaElement, double rate);
+        default void onPlaybackRateChange(@NonNull MediaElement mediaElement, double rate) {}
 
         /**
          * A media element has entered or exited fullscreen mode.
@@ -358,7 +362,7 @@ public class MediaElement {
          * @param fullscreen True if the media has entered full screen mode.
          */
         @UiThread
-        void onFullscreenChange(@NonNull MediaElement mediaElement, boolean fullscreen);
+        default void onFullscreenChange(@NonNull MediaElement mediaElement, boolean fullscreen) {}
 
         /**
          * An error has occurred.
@@ -368,7 +372,7 @@ public class MediaElement {
          *                  One of the {@link #MEDIA_ERROR_NETWORK_NO_SOURCE MEDIA_ERROR_*} flags.
          */
         @UiThread
-        void onError(@NonNull MediaElement mediaElement, @MediaErrorFlags int errorCode);
+        default void onError(@NonNull MediaElement mediaElement, @MediaErrorFlags int errorCode) {}
     }
 
     /* package */ long getVideoId() {
diff --git a/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/doc-files/CHANGELOG.md b/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/doc-files/CHANGELOG.md
index 11593bb2e7b0..0d85f21cf573 100644
--- a/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/doc-files/CHANGELOG.md
+++ b/mobile/android/geckoview/src/main/java/org/mozilla/geckoview/doc-files/CHANGELOG.md
@@ -88,6 +88,8 @@ exclude: true
 - Add missing `@Nullable` annotation to return value for
   `GeckoSession.PromptDelegate.ChoiceCallback.onPopupResult()`
 
+- Added `default` implementations for all non-functional `interface`s.
+
 ## v66
 - Removed redundant field `trackingMode` from [`SecurityInformation`][66.6].
   Use `TrackingProtectionDelegate.onTrackerBlocked` for notification of blocked
@@ -207,4 +209,4 @@ exclude: true
 [65.24]: ../CrashReporter.html#sendCrashReport-android.content.Context-android.os.Bundle-java.lang.String-
 [65.25]: ../GeckoResult.html
 
-[api-version]: 577c3b0d000b0b1da57f9af32331f1e9045939b9
+[api-version]: 09c473360eb5e17aa801fa0f966cd8671cf2f3d2