1. Plain install: Not blocked 2. With uBlock Origin: Blocked 3. Strict Enhanced Tracking Protection: Blocked 4. 2+3: Still blocked (unsurprisingly)
I would expect knowledgeable and concerned users (i.e. installing at least uBlock Origin) and people on systems managed by such people (e.g. family members of people in the first group who let that person manage their system) to be a higher percentage of Firefox users than other browsers.
I don't think Firefox has say a 10% share, but I do think that data derived from statcounter.com is going to underrepresent the share of Firefox users. As Google continues to make larger moves to fight ad-blocking, I expect that gap will widen.