Various UX fixes for esr 91.3

A couple of things in firefox CSS changed under us between esr91.2 and esr91.3 so those have been fixed (called out in #40684 (closed) ). We also noticed that we never updated a lot of the flat tor-browser icons with their thinner Proton'ified counterparts, so they have been updated as well as fixup!s for the relevant commits.

Fixes #40684 (closed)