If your workflow is how you like it I would stay.
Vaultwarden might be worth looking into when you have time or want to set it up to check it out. Self-hosted Bitwarden compatible server written in Rust. Lets you store OTP for free which is a convenience I enjoy.
I am thinking along the same lines. If they did remove it, they would probably try to make it a pain in the ass to add it back in, right? Certainly beyond my own abilities, however, I have faith someone would be able to do it!
Yep, it has Manifest v2 and v3 support. I believe Firefox supports Manifest v3. Manifest v2 was supposed to be removed* but Google has delayed it. From some quick searching, I was not able to find any firm date for v2 to be removed. I am with you though, when it does get removed, I will be strictly Firefox.
edit: updated a word
I use ungoogled-chromium with Firefox as a backup. The great thing about ungoogled-chromium is its a barebone browser, and that is exactly what I want. Only downfall is the browser does not auto update. I use change detector to get a notification when a new version is out.
Linux Mint