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.