Bug 203960: add a UI pref allowing the user to choose between "Add tabs" and "Replace existing tabs". r=Neil, sr=bryner

suite/common/bookmarks/bookmarks.js

@@ -590,7 +590,9 @@ var BookmarksCommand = {
           ++index;
         }
       }
-      browser.loadGroup(URIs);
+      var tab = browser.loadGroup(URIs);
+      if (!PREF.getBoolPref("browser.tabs.loadInBackground"))
+        browser.selectedTab = tab;
     } else {
       dump("Open Group in new window: not implemented...\n");
     }