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

suite/browser/navigator.js

@@ -878,7 +878,9 @@ function BrowserHome()
     for (var i in homePage)
       URIs.push({URI: homePage[i]});
 
-    gBrowser.loadGroup(URIs);
+    var tab = gBrowser.loadGroup(URIs);
+    if (!pref.getBoolPref("browser.tabs.loadInBackground"))
+      gBrowser.selectedTab = tab;
   }
 }