Bug 1228518 - Don't send SessionStore:update for initial about:blank page load. r=ttaubert

--HG--
extra : commitid : 6stWXZ9IUIJ
extra : rebase_source : c9dd1b4f641320ab0229097c868c216df5e96bce

browser/components/sessionstore/FrameTree.jsm

@@ -219,6 +219,15 @@ FrameTreeInternal.prototype = {
       return;
     }
 
+    // onStateChange will be fired when loading the initial about:blank URI for
+    // a browser, which we don't actually care about. This is particularly for
+    // the case of unrestored background tabs, where the content has not yet
+    // been restored: we don't want to accidentally send any updates to the
+    // parent when the about:blank placeholder page has loaded.
+    if (!this._chromeGlobal.docShell.hasLoadedNonBlankURI) {
+      return;
+    }
+
     if (stateFlags & Ci.nsIWebProgressListener.STATE_START) {
       // Clear the list of frames until we can recollect it.
       this._frames.clear();