Migrate to Tor Browser 6.0.x based on Firefox 45.2

Originally created by @anonym on #11403 (Redmine)

The Tor Browser that will be published at the same time as Tails 2.4 will be version 6.x, based on Firefox 45.2.

Feature Branch: feature/11403-tor-browser-6.x

Edited May 15, 2020 by anonym

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