Fortunately, the MV3 implementation in Firefox has the necessary tweaks to continue supporting add-ons like uBlock Origin[1]. So, even when MV2 is eventually dropped in Firefox, ad-blocking add-ons written for Firefox will continue to be able to work without restrictions.

[1] https://adguard.com/en/blog/firefox-manifestv3-chrome-adbloc...

Manifest V3 is mostly a good idea. Global variables only live for a few minutes, so extensions have to keep state in a key-value store instead. The code is more tedious, but this also helps extensions run well on Firefox for Android, where the OS kills processes at random.

The main problem with Manifest V3 is that Google used the API version bump as an opportunity to remove the 'blocking webRequest' API from Chrome. Firefox is keeping the API:

https://blog.mozilla.org/addons/2022/11/17/manifest-v3-signi...