--- a/toolkit/content/widgets/scrollbox.xml
+++ b/toolkit/content/widgets/scrollbox.xml
@@ -457,16 +457,21 @@
             }, 0);
           });
         ]]></body>
       </method>
     </implementation>
 
     <handlers>
       <handler event="wheel"><![CDATA[
+        // Don't consume the event if we can't scroll.
+        if (this.hasAttribute("notoverflowing")) {
+          return;
+        }
+
         let doScroll = false;
         let instant;
         let scrollAmount = 0;
         if (this.orient == "vertical") {
           doScroll = true;
           if (event.deltaMode == event.DOM_DELTA_PIXEL)
             scrollAmount = event.deltaY;
           else if (event.deltaMode == event.DOM_DELTA_PAGE)