--- a/browser/components/search/content/searchbar.js
+++ b/browser/components/search/content/searchbar.js
@@ -783,17 +783,22 @@
 
           document.popupNode = null;
 
           let { width } = this.getBoundingClientRect();
           // Ensure the panel is wide enough to fit at least 3 engines.
           if (this.oneOffButtons) {
             width = Math.max(width, this.oneOffButtons.buttonWidth * 3);
           }
+
+          // The CSS minWidth is necessary for the searchbar to be the correct
+          // width in the overflow menu. The width attribute is necessary for
+          // _invalidate().
           popup.style.minWidth = width + "px";
+          popup.setAttribute("width", width);
 
           popup._invalidate();
 
           popup.openPopup(this, "after_start");
         }
       };
 
       this.textbox.openSearch = () => {