--- a/browser/base/content/tabbrowser.xml
+++ b/browser/base/content/tabbrowser.xml
@@ -51,20 +51,18 @@
         }
 
         tabs._positionPinnedTabs();
       ]]></handler>
       <handler event="overflow"><![CDATA[
         // Ignore overflow events:
         // - from nested scrollable elements
         // - for vertical orientation
-        // - when the window is tiny initially
         if (event.originalTarget != this._scrollbox ||
-            event.detail == 0 ||
-            window.outerWidth <= 1) {
+            event.detail == 0) {
           return;
         }
 
         var tabs = document.getBindingParent(this);
         tabs.setAttribute("overflow", "true");
         tabs._positionPinnedTabs();
         tabs._handleTabSelect(true);
       ]]></handler>

--- a/toolkit/content/widgets/scrollbox.xml
+++ b/toolkit/content/widgets/scrollbox.xml
@@ -565,19 +565,17 @@
 
         this.setAttribute("notoverflowing", "true");
         this._updateScrollButtonsDisabledState();
       ]]></handler>
 
       <handler event="overflow" phase="capturing"><![CDATA[
         // Ignore overflow events:
         // - from nested scrollable elements
-        // - when the window is tiny initially
-        if (event.target != this ||
-            window.outerWidth <= 1) {
+        if (event.target != this) {
           return;
         }
 
         // Ignore events that doesn't match our orientation.
         // Scrollport event orientation:
         //   0: vertical
         //   1: horizontal
         //   2: both