You might want to check Firefox' telemetry settings if you care about privacy. Or you can use Librewolf, it's an extension-compatible FF fork with privacy turned on.
Librewolf is great, but from my experience the default settings are painful for daily use. My biggest gripe is the auto-clear cookies on restart. I understand why it could be useful to some users, but for most I doubt they'd want that in a daily browser. This makes Librewolf need tweaking just as much as Firefox does which kind of ruins the point of it in my experience. (although you are tweaking for usability rather than privacy)
Clearing cookies automatically is good for your privacy though and is a sensible default for a "hardened" configuration. If you use the password manager logging in again when you want to shouldn't be an issue.
