It's not financially worth supporting, Firefox has 6.53% of desktop and 0.53% of mobile marketshare (Statcounter), with a switching cost of zero if users encounter a breaking issue.
Not surprising it got to this point, Mozilla has been stagnant on features most users care about and catered exclusively to the privacy crowd for years - which isn't a large group and competes with Chromium offshoots (giving it a smaller niche, privacy but demanding an alternative rendering engine).
Sure, but the QA cost to support Firefox is significantly higher than the small fraction of people that will refuse to use a site that doesn't support it when they encounter an issue.
> catered exclusively to the privacy crowd for years
Not even that. Firefox on iOS doesn’t have an integrated adblocker. It’s been requested for years at this point, and browsers like Brave do have one. Pure unwillingness. It’s why I got all my non-techie family and friends to switch to Brave.
Not surprising it got to this point, Mozilla has been stagnant on features most users care about and catered exclusively to the privacy crowd for years - which isn't a large group and competes with Chromium offshoots (giving it a smaller niche, privacy but demanding an alternative rendering engine).