I think the metrics actually show that most users don't use extensions. But of the group that do use extensions, I'd guess an adblocker is the top one.
The question is - _an_ adblocker or _the_ adblocker (ublock)? As a long time FF Android user I prefer uMatrix and will wait with upgrade, hoping they fix this quickly. Otherwise... Not sure what I'll do. This is bad. :-(
As far as I know, uMatrix is not a (dynamic) ad blocker. That is, if some requests to subdomain.domain.net are for ads and some of the requests are for important page content, uMatrix isn't capable of distinguishing between the two. A real ad blocker uses block lists compiled (at least in part) by other people that can distinguish between two different URLs on the same domain.
Fair point, except - I am more concerned with tracking than the ads themselves. Which means I want to block Google fonts anywhere, and only allow domains when I want to. So no, I prefer uMatrix approach.