I'm already using Manifest V3 in Firefox for a few personal private addons that I develop, and I can confirm that blocking network requests already work perfectly fine in it. The only issues I have with Manifest V3 in Firefox are technical, I haven't noticed any issues that I think are problems of direction.

Firefox's Manifest V3 implementation arguably isn't ready for prime time (it has some pretty egregious bugs), but whenever they finally do get around to dropping Manifest V2 (which I have no idea when that would happen), I'm not really worried about extensions not being able to jump over.