Make test suite robust with Tor Browser 9.0

I see lots of failures which seem to be clear test suite robustness regressions triggered by the upgrade to Tor Browser 9.
This makes it hard to tell what else we need to do on #16356 (closed), and whether TB 9 fixes #17007.

Parent Task: #16356 (closed)

Related issues

Related to #17121 (closed)
Blocks #16209

Original created by @intrigeri on 17056 (Redmine)

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