Bug 1473253 - Stop setting onerror attribute on tabs. r=dao

browser/base/content/tabbrowser.js

@@ -2231,8 +2231,6 @@ window._gBrowser = {
       ContextualIdentityService.setTabStyle(t);
     }
 
-    t.setAttribute("onerror", "this.removeAttribute('image');");
-
     if (aSkipBackgroundNotify) {
       t.setAttribute("skipbackgroundnotify", true);
     }

browser/base/content/tabbrowser.xml

@@ -111,7 +111,6 @@
 
           var tab = this.firstChild;
           tab.label = this.emptyTabTitle;
-          tab.setAttribute("onerror", "this.removeAttribute('image');");
 
           window.addEventListener("resize", this);