alt Hacker NewsWatefox, Librewolf have both plucked out all unnecessary stuff Mozilla added over the years. Both are good but Librewolf comes with history and cache disabled by default which may be bit surprising.
Floorp comes with additional custom interface features, workspaces (tabs grouping) and mouse gestures. And bit better profiles feature - Mozilla decided to redo it recently which lead to some problems.
Mullvad has build in VPN, DoH and proxy as an extension, and comes with uBo and NoScript.
There's Zen browser that has a quite uncommon UI, and obscure Pale Moon that IIRC still tries to provide old XUL/XPCOM extensions - which often leads to pages rendering issues.
A tip for Librewolf: you can easily toggle permanent cookie storage for a site through the "Always store cookies/data for this site" option in the shield button menu on the URL bar. This is very convenient compared to vanilla Firefox where you have to add exceptions through the settings.