Bug 919532 - Make sure we don't lose state when quitting early without being notified; r=yoric

browser/components/sessionstore/src/SessionStore.jsm

@@ -2462,12 +2462,19 @@ let SessionStoreInternal = {
       delete this._statesToRestore[aWindow.__SS_restoreID];
       delete aWindow.__SS_restoreID;
       delete this._windows[aWindow.__SSi]._restoring;
-
-      // It's important to set the window state to dirty so that
-      // we collect their data for the first time when saving state.
-      DirtyWindows.add(aWindow);
     }
 
+    // It's important to set the window state to dirty so that
+    // we collect their data for the first time when saving state.
+    DirtyWindows.add(aWindow);
+
+    // Set the state to restore as the window's current state. Normally, this
+    // will just be overridden the next time we collect state but we need this
+    // as a fallback should Firefox be shutdown early without notifying us
+    // beforehand.
+    this._windows[aWindow.__SSi].tabs = aTabData.slice();
+    this._windows[aWindow.__SSi].selected = aSelectTab;
+
     if (aTabs.length == 0) {
       // this is normally done in restoreHistory() but as we're returning early
       // here we need to take care of it.