diff --git a/browser/themes/shared/customizableui/panelUIOverlay.inc.css b/browser/themes/shared/customizableui/panelUIOverlay.inc.css
index fafdee5a741a..acaf0c4dca4a 100644
--- a/browser/themes/shared/customizableui/panelUIOverlay.inc.css
+++ b/browser/themes/shared/customizableui/panelUIOverlay.inc.css
@@ -18,9 +18,9 @@
 %include ../browser.inc
 
 #PanelUI-button {
-  background-image: -moz-linear-gradient(hsla(0,0%,100%,0), hsla(0,0%,100%,.3) 30%, hsla(0,0%,100%,.3) 70%, hsla(0,0%,100%,0)),
-                    -moz-linear-gradient(hsla(210,54%,20%,0), hsla(210,54%,20%,.3) 30%, hsla(210,54%,20%,.3) 70%, hsla(210,54%,20%,0)),
-                    -moz-linear-gradient(hsla(0,0%,100%,0), hsla(0,0%,100%,.3) 30%, hsla(0,0%,100%,.3) 70%, hsla(0,0%,100%,0));
+  background-image: linear-gradient(to bottom, hsla(0,0%,100%,0), hsla(0,0%,100%,.3) 30%, hsla(0,0%,100%,.3) 70%, hsla(0,0%,100%,0)),
+                    linear-gradient(to bottom, hsla(210,54%,20%,0), hsla(210,54%,20%,.3) 30%, hsla(210,54%,20%,.3) 70%, hsla(210,54%,20%,0)),
+                    linear-gradient(to bottom, hsla(0,0%,100%,0), hsla(0,0%,100%,.3) 30%, hsla(0,0%,100%,.3) 70%, hsla(0,0%,100%,0));
   background-size: 1px calc(100% - 1px), 1px calc(100% - 1px), 1px  calc(100% - 1px) !important;
   background-position: 0px 0px, 1px 0px, 2px 0px;
   background-repeat: no-repeat;