I make use of Mullvad as a default browser. I will say there was a bit of an adjustment getting accustomed to what sites work and what didn’t. I use a hardened FireFox for things involving video.
I do not use a password extension on any of the browsers I use. I often do not log into sites because I am not interested in or need the personalized attention/interaction and have no interest in making data collection easier. Only recently, after a decent amount of time using Mullvad, did I run into an issue in which I had to change my default browser to Firefox for a situation, but, that was not much of an issue switch and return back.