This is an excellent analogy.

Personally I'm surprised by Google's attitude to a11y/Firefox because all their products have millions of users. 10% doesn't sound like much, but 10% (Firefox market share) of 50 million is more than the population of many countries.

I guess they rationalise it by saying "our product is new, with 0 users right now. Let's focus on the largest segments of users (Chrome, non-a11y) and ship an MVP. If it sticks, let's expand to Firefox, do the a11y work etc." If I was in that PM's shoes, this makes sense to me. As a user ... it feels wrong.