Bug 1147487 - Don't try to reader-ize non-HTML documents. r=margaret, r=jaws, a=lmandel

toolkit/components/reader/ReaderMode.jsm

@@ -118,8 +118,12 @@ this.ReaderMode = {
    * @return boolean Whether or not we should show the reader mode button.
    */
   isProbablyReaderable: function(doc) {
-    let uri = Services.io.newURI(doc.location.href, null, null);
+    // Only care about 'real' HTML documents:
+    if (doc.mozSyntheticDocument || !(doc instanceof doc.defaultView.HTMLDocument)) {
+      return false;
+    }
 
+    let uri = Services.io.newURI(doc.location.href, null, null);
     if (!this._shouldCheckUri(uri)) {
       return false;
     }