A place to discuss the news and latest developments on the open-source browser Firefox
Mozilla doesn't sell your data, and I've never heard any news about Firefox Sync having a breach, your data is safe from attackers and Mozilla themselves with Sync.
https://support.mozilla.org/en-US/kb/how-firefox-sync-keeps-your-data-safe-even-if-tls-fails
The data is encrypted, so not even Mozilla can see the data you sync, and Mozilla is also generally pretty trustworthy, so in terms of privacy, its fine.
For passwords, its probably not as secure as trusted dedicated password managers like Bitwarden. I just use Firefox for syncing bookmarks and sometimes tabs, and Bitwarden for passwords and things like that.
I trust personally trust them but if you don't, you can self host the sync server if I'm not mistaken.
You can indeed: https://mozilla-services.readthedocs.io/en/latest/howtos/run-sync-1.5.html https://mozilla-services.readthedocs.io/en/latest/howtos/run-fxa.html
I've not tried it but looks doable but probably need a degree of familiarity with both web hosting and linux based systems to trouble shoot, and you need to run both Sync and Accounts to authenticate it.
Personally I do trust Firefox with my browsing data and syncing so use their service.
They don't sell your usage data or anything like that, but I still don't trust a browser to save things like passwords. There are better, more secure options for that sort of thing.