Maybe I'm reading this wrong, but from the graphs it seems like there's been barely a change in the last few years? I wouldn't call that fast.
"Firefox user activity" would be better.
2014: 1.29 billion
2015: 1.54 billion
2016: 1.88 billion
2017: 2.07 billion
2018: 2.40 billion
2019: 2.64 billion
2020: 2.65 billion
https://backlinko.com/chrome-users
Not that much gained recently it seems. Can't find a good source for 2021 and 2022, but looking at some it may have actually decreased too during that time.