alt Hacker NewsIt's not impossible that people would pay Firefox that much yearly to keep their current user-base from using ad blockers. However, what is impossible is to imagine Firefox would have anything close to their current user base if people were prevented from using ad blockers. Most likely they would shrink to almost 0 users overnight if they did this. There are very few reasons to use Firefox over Chrome or Safari (or even Edge) other than the much better ad blocking (or any ad blocking, on mobile).
That doesn't explain the apparent market share of 2--3%, which is still quite large if you think about.
I believe most non-techie users are just lingering, using Firefox just because they used to. Since Firefox doesn't have a built-in ad blocking and the knowledge about adblocking is not universal (see my other comment), it is possible that there are a large portion of Firefox users who don't use adblockers and conversely adblocking users are in a minority. If this is indeed the case, Mozilla can (technically) take such a bet as such policy will affect a smaller portion of users. But that would work only once; Mozilla doesn't have any more option like that after all. That's why I see $150M is plausible, but only once.