Does anyone have an idea of how to do it or even if it’s possible? Because as I am paranoid I would like to close my Mozilla account.
BONUS: How to prevent the installation of new extensions from opening welcome pages because it’s very annoying thank you.
You can host a Firefox sync server yourself. You could run that on something like a Raspberry Pi in your local network. If you need remote access, use something like cloudflare tunnels (although I guess that’s something else to be paranoid about).
It’s quite difficult to get it running. The latest version is impossible.
I wrote some documentation and a docker compose to make it a bit easier:
https://github.com/jeena/fxsync-docker
Thank you for doing this