Check for possible extension conflicts with TorBirdy

Bry8Star reports on IRC that when using the "Tweekilla", "New Account Types" and "WebApp Tabs" extensions, that there was a conflict when TorBirdy was disabled or uninstalled.

It should not be related to us since we are not touching other extensions, but still we should check to make sure that there isn't a bug anywhere else.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information