diff --git a/dom/base/nsContentUtils.cpp b/dom/base/nsContentUtils.cpp
index 058b7f236663..a12d958ab305 100644
--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -264,6 +264,7 @@ nsString* nsContentUtils::sModifierSeparator = nullptr;
 
 bool nsContentUtils::sInitialized = false;
 bool nsContentUtils::sIsFullScreenApiEnabled = false;
+bool nsContentUtils::sIsUnprefixedFullscreenApiEnabled = false;
 bool nsContentUtils::sTrustedFullScreenOnly = true;
 bool nsContentUtils::sIsCutCopyAllowed = true;
 bool nsContentUtils::sIsFrameTimingPrefEnabled = false;
@@ -539,6 +540,9 @@ nsContentUtils::Init()
   Preferences::AddBoolVarCache(&sIsFullScreenApiEnabled,
                                "full-screen-api.enabled");
 
+  Preferences::AddBoolVarCache(&sIsUnprefixedFullscreenApiEnabled,
+                               "full-screen-api.unprefix.enabled");
+
   Preferences::AddBoolVarCache(&sTrustedFullScreenOnly,
                                "full-screen-api.allow-trusted-requests-only");
 
diff --git a/dom/base/nsContentUtils.h b/dom/base/nsContentUtils.h
index c4c3a3aa6674..775b6a7b168c 100644
--- a/dom/base/nsContentUtils.h
+++ b/dom/base/nsContentUtils.h
@@ -1912,6 +1912,12 @@ public:
    */
   static bool IsFullScreenApiEnabled();
 
+  /**
+   * Returns true if the unprefixed fullscreen API is enabled.
+   */
+  static bool IsUnprefixedFullscreenApiEnabled()
+    { return sIsUnprefixedFullscreenApiEnabled; }
+
   /**
    * Returns true if requests for full-screen are allowed in the current
    * context. Requests are only allowed if the user initiated them (like with
@@ -2661,6 +2667,7 @@ private:
   static bool sIsHandlingKeyBoardEvent;
   static bool sAllowXULXBL_for_file;
   static bool sIsFullScreenApiEnabled;
+  static bool sIsUnprefixedFullscreenApiEnabled;
   static bool sTrustedFullScreenOnly;
   static bool sIsCutCopyAllowed;
   static uint32_t sHandlingInputTimeout;
diff --git a/dom/base/nsDocument.cpp b/dom/base/nsDocument.cpp
index 1cae937b2984..2b0f649b027e 100644
--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -11680,6 +11680,14 @@ nsresult nsDocument::RemoteFrameFullscreenReverted()
   return NS_OK;
 }
 
+/* static */ bool
+nsDocument::IsUnprefixedFullscreenEnabled(JSContext* aCx, JSObject* aObject)
+{
+  MOZ_ASSERT(NS_IsMainThread());
+  return nsContentUtils::IsCallerChrome() ||
+         nsContentUtils::IsUnprefixedFullscreenApiEnabled();
+}
+
 static void
 ReleaseVRDeviceProxyRef(void *, nsIAtom*, void *aPropertyValue, void *)
 {
diff --git a/dom/base/nsDocument.h b/dom/base/nsDocument.h
index 5167e07d6a59..60f1237c6226 100644
--- a/dom/base/nsDocument.h
+++ b/dom/base/nsDocument.h
@@ -1236,6 +1236,8 @@ public:
   //
   already_AddRefed<nsSimpleContentList> BlockedTrackingNodes() const;
 
+  static bool IsUnprefixedFullscreenEnabled(JSContext* aCx, JSObject* aObject);
+
   // Do the "fullscreen element ready check" from the fullscreen spec.
   // It returns true if the given element is allowed to go into fullscreen.
   bool FullscreenElementReadyCheck(Element* aElement, bool aWasCallerChrome);
diff --git a/dom/webidl/Document.webidl b/dom/webidl/Document.webidl
index 67e461637309..40f17f1aa5bd 100644
--- a/dom/webidl/Document.webidl
+++ b/dom/webidl/Document.webidl
@@ -224,13 +224,16 @@ partial interface Document {
 partial interface Document {
   // Note: Per spec the 'S' in these two is lowercase, but the "Moz"
   // versions hve it uppercase.
+  [Func="nsDocument::IsUnprefixedFullscreenEnabled"]
   readonly attribute boolean fullscreenEnabled;
   [BinaryName="fullscreenEnabled", Deprecated="PrefixedFullscreenAPI"]
   readonly attribute boolean mozFullScreenEnabled;
+  [Func="nsDocument::IsUnprefixedFullscreenEnabled"]
   readonly attribute Element? fullscreenElement;
   [BinaryName="fullscreenElement", Deprecated="PrefixedFullscreenAPI"]
   readonly attribute Element? mozFullScreenElement;
 
+  [Func="nsDocument::IsUnprefixedFullscreenEnabled"]
   void exitFullscreen();
   [BinaryName="exitFullscreen", Deprecated="PrefixedFullscreenAPI"]
   void mozCancelFullScreen();
diff --git a/dom/webidl/Element.webidl b/dom/webidl/Element.webidl
index 1e2da94a9dd7..3eb36bbab549 100644
--- a/dom/webidl/Element.webidl
+++ b/dom/webidl/Element.webidl
@@ -259,7 +259,7 @@ partial interface Element {
    * The options parameter is non-standard. In Gecko, it can be:
    *  a RequestFullscreenOptions object
    */
-  [Throws, UnsafeInPrerendering]
+  [Throws, UnsafeInPrerendering, Func="nsDocument::IsUnprefixedFullscreenEnabled"]
   void requestFullscreen(optional any options);
   [Throws, UnsafeInPrerendering, BinaryName="requestFullscreen", Deprecated="PrefixedFullscreenAPI"]
   void mozRequestFullScreen(optional any options);
diff --git a/dom/webidl/EventHandler.webidl b/dom/webidl/EventHandler.webidl
index eba8c4acba90..d37851dda5ff 100644
--- a/dom/webidl/EventHandler.webidl
+++ b/dom/webidl/EventHandler.webidl
@@ -118,7 +118,9 @@ interface GlobalEventHandlers {
            attribute EventHandler onlostpointercapture;
 
            // Fullscreen events handlers
+           [Func="nsDocument::IsUnprefixedFullscreenEnabled"]
            attribute EventHandler onfullscreenchange;
+           [Func="nsDocument::IsUnprefixedFullscreenEnabled"]
            attribute EventHandler onfullscreenerror;
            attribute EventHandler onmozfullscreenchange;
            attribute EventHandler onmozfullscreenerror;