This doesn't fully describe situation, but over last 3 years, mobile users went from 50% to 75% users in my prev company's data. And Firefox is nowhere in those mobile stats.
Also, the market share numbers reported by client side trackers like StatsCounter are very close to log file collection and analysis by companies like Kinsta.
Sure, it's using Safari as a renderer, but these days that's hardly where the differentiating value is.
Even before the whole privacy focused thing FF was already in decline to sub 10% market on Desktop.
If you think about it the other way around, it is still hanging on to 5-10% of Desktop market after all is actually quite good. At its peak, Firefox was closing to 40% in some European countries. If you consider IE in Business Cooperate usage and Firefox are not available in those settings, 40% is a really big deal.
https://data.firefox.com/dashboard/user-activity
I’ve watched the decline for years, straight from the source. These usage numbers are not affected by privacy settings.
I was clearly wrong, though it is easy to change your user agent it's unlikely that many Firefox users have done it.
I'd add there is a large gap in usage between uBlock and Matrix. uBlock has over 10 million users whereas Matrix is somewhere over 100,000.