Hack...

common/content/events.js

@@ -905,7 +905,7 @@ function Events() //{{{
 
             try
             {
-                liberator.threadYield(false, true);
+                liberator.threadYield(1, true);
 
                 noremap = !!noremap;
 

common/content/liberator.js

@@ -1391,7 +1391,7 @@ const liberator = (function () //{{{
                 if (liberator.interrupted)
                     throw new Error("Interrupted");
             }
-            while (flush && mainThread.hasPendingEvents());
+            while (flush === true && mainThread.hasPendingEvents());
         },
 
         variableReference: function (string)