diff --git a/dom/base/nsContentUtils.cpp b/dom/base/nsContentUtils.cpp
index ca9d89298fc1..1e2d61fb7bc5 100644
--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -303,6 +303,7 @@ bool nsContentUtils::sSendPerformanceTimingNotifications = false;
 bool nsContentUtils::sUseActivityCursor = false;
 bool nsContentUtils::sAnimationsAPICoreEnabled = false;
 bool nsContentUtils::sAnimationsAPIElementAnimateEnabled = false;
+bool nsContentUtils::sAnimationsAPIPendingMemberEnabled = false;
 bool nsContentUtils::sGetBoxQuadsEnabled = false;
 bool nsContentUtils::sSkipCursorMoveForSameValueSet = false;
 bool nsContentUtils::sRequestIdleCallbackEnabled = false;
@@ -714,6 +715,10 @@ nsContentUtils::Init()
   Preferences::AddBoolVarCache(&sAnimationsAPIElementAnimateEnabled,
                                "dom.animations-api.element-animate.enabled", false);
 
+  Preferences::AddBoolVarCache(&sAnimationsAPIPendingMemberEnabled,
+                               "dom.animations-api.pending-member.enabled",
+                               false);
+
   Preferences::AddBoolVarCache(&sGetBoxQuadsEnabled,
                                "layout.css.getBoxQuads.enabled", false);
 
diff --git a/dom/base/nsContentUtils.h b/dom/base/nsContentUtils.h
index 72440e6d7ba6..956d5caf1230 100644
--- a/dom/base/nsContentUtils.h
+++ b/dom/base/nsContentUtils.h
@@ -2347,6 +2347,15 @@ public:
     return sAnimationsAPIElementAnimateEnabled;
   }
 
+  /**
+   * Returns true if the DOM Animations API should report a pending animation
+   * using the separate 'pending' member instead of the 'playState' member.
+   */
+  static bool AnimationsAPIPendingMemberEnabled()
+  {
+    return sAnimationsAPIPendingMemberEnabled;
+  }
+
   /**
    * Returns true if the getBoxQuads API should be enabled.
    */
@@ -3415,6 +3424,7 @@ private:
   static bool sUseActivityCursor;
   static bool sAnimationsAPICoreEnabled;
   static bool sAnimationsAPIElementAnimateEnabled;
+  static bool sAnimationsAPIPendingMemberEnabled;
   static bool sGetBoxQuadsEnabled;
   static bool sSkipCursorMoveForSameValueSet;
   static bool sRequestIdleCallbackEnabled;
diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index 405e5c45a750..f50c7d9f0d88 100644
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -3096,6 +3096,10 @@ pref("dom.animations-api.core.enabled", true);
 // ignored.
 pref("dom.animations-api.element-animate.enabled", true);
 
+// Is the pending state reported using a separate 'pending' member of the
+// Animation interface as opposed to the 'playState' member?
+pref("dom.animations-api.pending-member.enabled", false);
+
 // Pref to throttle offsreen animations
 pref("dom.animations.offscreen-throttling", true);