Mozilla neutered themselves when they 1) stuck with an ancient, bug-riddled, poorly performing codebase for too long, and 2) tripled down on the JS/HTML/CSS trifecta of suck, and 3) then tried to use it to build an OS.

Google was the only browser vendor actively trying to move the web stack beyond the technology swamp it's been mired in for so long.

There are individuals today who have literally built an entire career without seeing anything beyond the browser tech stack (a lot of them on HN -- note the downvotes), and Mozilla was champion #1 of that dismal reality.