Use SUMO "stop Firefox from making automatic connections" article to further vet default Firefox prefs

[stephendonner]

We should look through this SUMO article (among others - still looking!) and see if we can use it to help further vet/whittle down spurious, extraneous connection requests:

https://support.mozilla.org/en-US/kb/how-stop-firefox-making-automatic-connections

The aim is to see which -- if any -- additional Firefox prefs we should set/change, etc., over in wptagent