Upgrade to Tor Browser based on Firefox 68.2
This ticket is about importing the security update immediately before our release, while #16356 is about porting Tails to Tor Browser 9.0 (which must be completed earlier).
Revert "Test suite: update for the UI of Tor Browser 9's Tor Launcher" (refs: #16693)
Tor Launcher UI was fixed to allow entering multiple bridges again:
This reverts commit 5f6ffd72d4aa39b85ea48f51a945c7c635b2698c.