IronFox is a privacy fork for Android, the rest of these are meant for desktop.

Waterfox is privacy-focused but more focused on convenience than Librewolf*.

Librewolf is also privacy-focused but leans further into privacy than Waterfox with the sacrifice of convenience.

Mullvad Browser leans even further into privacy than Librewolf with the sacrifice of convenience. Made by the Tor team and Mullvad.

*I haven’t used Waterfox much but this seems to be the consensus online