According to these folks[0], Firefox has a 3.29% market share globally. They also claim there are 4.66 billion browser users globally.
If those numbers are correct, Firefox has a bit more than 150,000,000 users worldwide.
If my software had 150,000,000 users, I'd consider that wildly successful.
Other folks have different ideas/takes on that, I suppose. But it's food for thought nonetheless.
[0] https://backlinko.com/browser-market-share#worldwide-browser...
Edit: Fixed prose.