--- a/browser/components/BrowserGlue.jsm
+++ b/browser/components/BrowserGlue.jsm
@@ -2684,17 +2684,17 @@ BrowserGlue.prototype = {
       );
     });
   },
 
   // eslint-disable-next-line complexity
   _migrateUI: function BG__migrateUI() {
     // Use an increasing number to keep track of the current migration state.
     // Completely unrelated to the current Firefox release number.
-    const UI_VERSION = 85;
+    const UI_VERSION = 86;
     const BROWSER_DOCURL = AppConstants.BROWSER_CHROME_URL;
 
     let currentUIVersion;
     if (Services.prefs.prefHasUserValue("browser.migration.version")) {
       currentUIVersion = Services.prefs.getIntPref("browser.migration.version");
     } else {
       // This is a new profile, nothing to migrate.
       Services.prefs.setIntPref("browser.migration.version", UI_VERSION);
@@ -3075,16 +3075,35 @@ BrowserGlue.prototype = {
       const CUSTOM_BLOCKING_PREF =
         "browser.contentblocking.customBlockList.preferences.ui.enabled";
       // Check if user has set custom tables pref, and show custom block list UI
       // in the about:preferences#privacy custom panel.
       if (Services.prefs.prefHasUserValue(TRACKING_TABLE_PREF)) {
         Services.prefs.setBoolPref(CUSTOM_BLOCKING_PREF, true);
       }
     }
+
+    if (currentUIVersion < 86) {
+      // If the user has set "media.autoplay.allow-muted" to false
+      // migrate that to media.autoplay.default=BLOCKED_ALL.
+      if (
+        Services.prefs.prefHasUserValue("media.autoplay.allow-muted") &&
+        !Services.prefs.getBoolPref("media.autoplay.allow-muted") &&
+        !Services.prefs.prefHasUserValue("media.autoplay.default") &&
+        Services.prefs.getIntPref("media.autoplay.default") ==
+          Ci.nsIAutoplay.BLOCKED
+      ) {
+        Services.prefs.setIntPref(
+          "media.autoplay.default",
+          Ci.nsIAutoplay.BLOCKED_ALL
+        );
+      }
+      Services.prefs.clearUserPref("media.autoplay.allow-muted");
+    }
+
     // Update the migration version.
     Services.prefs.setIntPref("browser.migration.version", UI_VERSION);
   },
 
   _checkForDefaultBrowser() {
     // Perform default browser checking.
     if (!ShellService) {
       return;