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.
This is for what I have created a Extension called “SyncMarks”. It’s available for Firefox from AMO. The same exist for all Chromium based browser, including Chromium, Chrome, Edge and a lot more. For Edge its available in the Microsoft Edge Store, all others can sideload the extension. The extension is cross-browser compatible, so that you can sync bookmarks between Firefox and Chromium. As a backend for best results, you can use the PHP based backend for selhosting or any WebDAV as a alternative (not all functions available). Installation of the backend is super easy. You can find everything at Codeberg.
BTW. The PHP backend works as WebApp, so that you can access the bookmarks also, when the extension is not installed, from any browser.