Comment by acdha

Here’s another way to answer that question: do Vimeo, Twitch, Netflix, Amazon Prime, Instagram, TikTok, etc. say “let them use Chrome” or do they manage to do entry-level browser testing? The cost increase is nowhere near 50% and clearly they aren’t willing to write off millions of users – only the company with a direct financial incentive does that.

Yes, Firefox’s market share has been declining but that’s substantially because Google spent billions of dollars marketing Chrome and promoted it heavily on YouTube, Gmail, Search, etc. Deciding not to test or optimize fits neatly into the same pattern.