Bug 1710255 - Use instanceof to test nodes instead of getClassName(). r=darktrojan

--HG--
extra : histedit_source : f1bd866ac5ddebc28e2f2f896afefaace6e05427%2Ca5aa2896ed45b1b52a03e7b485f53bb7f1536f5d

mail/base/content/specialTabs.js

@@ -711,10 +711,7 @@ var specialTabs = {
     let onDownload = aEvent => {
       let request = aEvent.target;
       let dom = request.response;
-      if (
-        request.status != 200 ||
-        ChromeUtils.getClassName(dom) !== "HTMLDocument"
-      ) {
+      if (request.status != 200 || !(dom instanceof HTMLDocument)) {
         onDownloadError(aEvent);
         return;
       }

mailnews/extensions/newsblog/FeedParser.jsm

@@ -47,7 +47,7 @@ FeedParser.prototype = {
    *                    nothing to do condition.
    */
   parseFeed(aFeed, aDOM) {
-    if (ChromeUtils.getClassName(aDOM) !== "XMLDocument") {
+    if (!(aDOM instanceof XMLDocument)) {
       // No xml doc.
       aFeed.onParseError(aFeed);
       return [];