Fix torbutton for ESR45

domain-isolator.js has a couple of minor breakages in Firefox 45.

1. A new ReferenceError is thrown by things like let mozilla = mozilla || {};. We can change it to let mozilla = {};.

2. The method newSOCKSProxyInfo was available in our SOCKS proxy patch. Since we landed that patch with some minor changes, we should now make an equivalent call to built-in Firefox method newProxyInfoWithAuth.