--- a/browser/base/content/contentSearchUI.js
+++ b/browser/base/content/contentSearchUI.js
@@ -269,19 +269,21 @@ ContentSearchUIController.prototype = {
       searchString: searchTerms,
       healthReportKey: this._healthReportKey,
       searchPurpose: this._searchPurpose,
       originalEvent: {
         shiftKey: aEvent.shiftKey,
         ctrlKey: aEvent.ctrlKey,
         metaKey: aEvent.metaKey,
         altKey: aEvent.altKey,
-        button: aEvent.button,
       },
     };
+    if ("button" in aEvent) {
+      eventData.originalEvent.button = aEvent.button;
+    }
 
     if (this.suggestionAtIndex(this.selectedIndex)) {
       eventData.selection = {
         index: this.selectedIndex,
         kind: undefined,
       };
       if (aEvent instanceof MouseEvent) {
         eventData.selection.kind = "mouse";