if you want a newer firefox use flatpak, don't pollute your system with unofficial debs or source installs

These kinds of statements suit servers with high availability requirements but really shouldn’t be made without context. Adding the Mozilla Debian Firefox repos probably won’t break anything catastrophic, and the time cost / risk of containers is non zero too.

I’ve had more trouble and time wasted with snap Firefox than I’ve had with official Mozilla repos under both Debian and Ubuntu.

flatpak is not snap

The point still stands.

it doesn't because flatpak has basically zero of the problems that snap has (slow app start, forced updates ...). It just works and keeps your system clean.

Firefox is the one app that I want in my base system. Maybe it’s better now, but I always seem to run into some issue with the Flatpak. Usually because some other Flatpak app wants to log in and something goes wrong between all the redirects between the apps that that entails.

The Mozilla Firefox-Repo is really a bad example for convincing people to go away using Debian package repos: You can even install Firefox-ESR and Firefox Stable and Firefox Beta (and maybe Firefox Nightly, haven't tested it) from the Debian- and Mozilla- Repos in parallel.