There are good solid reasons why Manifest v3 is preferable for most extensions.
The issue is that adblocking doesn't work with it, so an addition, or workaround should be made, but when Google has the amount of influence they have, that didn't happen.
The upshut is that people hate ads and like free stuff, so there is now a good selling point for Firefox. Hell some of us switched to Firefox because it blocked popup ads and had tabs, back in the day.
> The issue is that adblocking doesn't work with it
Except this is objectively not true…
uBlock Origin Lite is nearly as good as uBO and blocks nearly everything except for mostly Twitch ads.
Manifest v3 is a big security upgrade and effectively closes off the permanent RCE pathway that v2 allowed.