diff --git a/browser/base/content/tabbrowser.xml b/browser/base/content/tabbrowser.xml
index f95c39b5617..3fcf1be2a78 100644
--- a/browser/base/content/tabbrowser.xml
+++ b/browser/base/content/tabbrowser.xml
@@ -2547,6 +2547,11 @@
         if (event.target != this)
           return;
 
+        // Ignore vertical events.
+        if (event.detail == 0) {
+          return;
+        }
+
         this._scrollButtonDownBox.collapsed = true;
         this._scrollButtonDownBoxAnimate.collapsed = true;
       ]]></handler>
@@ -2556,6 +2561,11 @@
         if (event.target != this)
           return;
 
+        // Ignore vertical events.
+        if (event.detail == 0) {
+          return;
+        }
+
         this._scrollButtonDownBox.collapsed = false;
         this._scrollButtonDownBoxAnimate.collapsed = false;
       ]]></handler>