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.
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.