--- a/browser/themes/shared/customizableui/panelUI.inc.css
+++ b/browser/themes/shared/customizableui/panelUI.inc.css
@@ -468,16 +468,17 @@ photonpanelmultiview .panel-subview-body
   width: calc(@menuPanelButtonWidth@);
   height: calc(51px + 2.2em);
 }
 
 .animate-out {
   animation-name: widget-animate-out;
   animation-fill-mode: forwards;
   animation-duration: 500ms;
+  animation-timing-function: var(--animation-easing-function);
 }
 
 @keyframes widget-animate-out {
   0% {
     opacity: 1;
     transform: scale(1);
   }
   100% {