Chromium based browsers have the strongest sandbox implementation among desktop browsers (also on mobile). Firefox is far less secure in this regard. In fact, you have to distinguish between privacy and security - which is more important to you? If you do not trust anything Google then you might prefer to stay away from chromium based browsers even though that might put you in a less secure position, browser wise. Brave and arguably Vivaldi, both chromium based browsers, are solid choices for standard users, I guess.
If privacy is paramount to you, you might prefer the Tor Browser or other projects that focus on exactly this one thing - privacy with a clear strategy in mind.
Further reading: