Bug 1317697: Fix reference to undefined property warnings. r=mixedpuppy

MozReview-Commit-ID: vngYhAOgbV --HG-- extra : rebase_source : c25f29d510549ff41b21f7fcf20f1f48ae0d794a
2017-04-13 15:10:23 -07:00 · 2017-04-13 15:10:23 -07:00 · b8f0f730da
--- a/toolkit/content/widgets/browser.xml
+++ b/toolkit/content/widgets/browser.xml
@ -390,10 +390,11 @@
      <method name="getTabBrowser">
        <body>
          <![CDATA[
-            var tabBrowser = this.parentNode;
-            while (tabBrowser && tabBrowser.localName != "tabbrowser")
-              tabBrowser = tabBrowser.parentNode;
-            return tabBrowser;
+            for (let node = this.parentNode; node instanceof Element; node = node.parentNode) {
+              if (node.localName == "tabbrowser")
+                return node;
+            }
+            return null;
          ]]>
        </body>
      </method>