Firefox is supporting Manifest v3 extensions however they are not imposing every limitation Chrome is on them and they are continuing to support features outside the scope of v3 like blocking webrequest.

A lot of the changes in v3 are actually pretty sensible, it's just 10% of the stuff shoehorned in creating 90% of the friction.

https://blog.mozilla.org/addons/2021/05/27/manifest-v3-updat...