Check HTTP requests from add-ons
We are preventing add-ons from auto-updating but the console logs this:
1417114612642 addons.update-checker WARN HTTP Request failed for an unknown reason
1417114615860 addons.update-checker WARN Update manifest for {972ce4c6-7e08-4474-a285-3208198ce6fd} did not contain an updates property
1417114616416 addons.update-checker WARN Update manifest for ctypes-otr@tormessenger did not contain an updates property
So while the request fails, it still makes the request. We should check this.