It has included some privacy measures to resist fingerprinting like letterboxing and has more privacy focused search engines as default like searx. Also it takes out some firefox utilities like pocket which I don’t really use
As for Mullwav browser I’m not really sure, it seems to be another reinforced firefox like librewolf
For incognito browsing I recommend Librewolf, a firefox fork. If you want anything more secure, you should start looking into tor
I usually use the “add non-steam games” utility with the game’s executable and then modify the compatibility options of the added game.