alt Hacker NewsThere's a lot of opinions and anecdata in that. Firefox was almost never as bad as it was marketed to be (by its competition), and Chrome was certainly never as good as it was marketed to be (by an evil ad company pretending to be a good, well adjusted internet benefit company).
I don't know why people left Firefox, but I know why *I* did. And it was three or four years ago (after using it for 15 years) because I got annoyed at them for removing many features that I used over the years, and because I tried a Crommium based browser and it just had better performance and better ad-blocking. That's just one anecdote, but feel free to correlate it with other anecdotes to find some patterns and reach your own conclusion.