Fix JS error when this.sender.tab is undefined

background/background.js

@@ -43,6 +43,7 @@ window.API_METHODS = Object.assign(window.API_METHODS || {}, {
   openEditor,
 
   updateIconBadge(count) {
+    if (this.sender.tab) {
       // TODO: remove once our manifest's minimum_chrome_version is 50+
       // Chrome 49 doesn't report own extension pages in webNavigation apparently
       // so we do a force update which doesn't use the cache.
@@ -51,6 +52,7 @@ window.API_METHODS = Object.assign(window.API_METHODS || {}, {
       } else {
         updateIconBadge(this.sender.tab.id, count);
       }
+    }
     return true;
   },