alt Hacker NewsThat 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.
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Ad-blockers are the most used extensions on firefox. Origin itself has 10m installs, there are others with 3m and few with 1m installs.
Of course, I don't know the actual percent of FF users that use ad block. But I think it's far more likely that it is a majority of current FF users, rather than it being a negligible minority. I think 2-3% of web users is not an implausible approximation of how many people use ad block overall on the web. It's not an obscure technology, it's quite well known, even if few people bother with it.
Edit: actually I'm way off - it seems estimates are typically around 30-40% of overall users on the web having some kind of ad blocker. So, the Firefox percentage being 60-80+% seems almost a given to me.