I’d been using Firefox on desktop for years and years (excluding the Macbook I had when I was working on my masters, where I used Safari).
The main reason I switched to Firefox on Android was Chrome insisted on displaying tabs in grid view, which drove me nuts. After switching, I started to learn more about privacy and concerns about corporations like Google and Microsoft exerting too much control over the internet and how we use it. Now I use Fennec on Android, and on desktop I use Firefox proper, Librewolf, and Tor, depending on what I’m doing and what level of functionality I need.
I’m also gradually migrating from Windows to Linux on my personal machines.