After a couple days of regular Web browsing on two different computers running Debian Sid, the silent add-on disabling did not happen again. I marked this bug as fixed in version 85.0.1-1 since no one reported otherwise, but feel free to chime in if you actually still get this issue with 85.0.1-1 (or newer).
OpenPGP_signature
Description: OpenPGP digital signature
