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.
It works for me. Be sure that you have selected add-ons in the sync options.
All except the Logins and Credit cards option is selected. It did not work when I moved from Firefox to Icecat, or IceCat to LibreWolf. I had to install the addons manually.
Were Flatpaks, Snaps or AppImages involved ?
None of them. I was on the system’s package manager.
I have no idea how sync works. On non Mozilla Firefox but it works great on normal Firefox.