--- a/toolkit/content/widgets/videocontrols.xml
+++ b/toolkit/content/widgets/videocontrols.xml
@@ -1673,17 +1673,17 @@
 
         // Use flexible spacer to separate controls when scrubber is hidden.
         // As long as muteButton hidden, which means only play button presents,
         // hide spacer and make playButton centered.
         this.controlBarSpacer.hidden = !this.scrubberStack.hidden || this.muteButton.hidden;
 
         // Since the size of videocontrols is expanded with controlBar in <audio>, we
         // should fix the dimensions in order not to recursively trigger reflow afterwards.
-        if (this.isAudioOnly) {
+        if (this.video instanceof HTMLAudioElement) {
           if (givenHeight) {
             this.controlBar.style.height = `${Math.max(givenHeight, this.controlBarMinVisibleHeight)}px`;
           }
           this.controlBar.style.width = `${videoWidth - minControlBarPaddingWidth}px`;
           return;
         }
 
         if (videoHeight < this.controlBarMinHeight ||