That list contains issues with the APIs that Chrome exposes via MV3. Firefox still supports APIs that Chrome removed.

Not really, but this FAQ, like almost all articles published on MV3, conflates MV3 the specification with Chrome's MV3 implementation. (FWIW, I'm almost certain that this is either due to sloppy/imprecise writing or intentional, with the authors not wanting to confuse users already appropriately riled up by equally imprecise reporting on MV3. They definitely know the difference.)

In any case, for better or worse, when people say MV3, they now usually mean "Chrome's MV3 implementation", which obviously never applies to Firefox.