I've been using FireFox for about 4.5 years now, but I have to have Chrome installed for a few reasons unfortunately.
- Some websites still will just not work in FireFox. It's not super common anymore, but if I sense something is fishy, I pop open the console and see some strange error and swap over to Chrome. Things will just work then. All extensions disabled even. I even ran into this on Vanguard's website, albeit for some obscure forms.
- When I worked at a company that had a larger web app presence, I would have to test in Chrome. That's a given, but my Chrome counterparts did not do the same with FireFox. I would fairly regularly (few times a quarter) find things that were completely broked on FireFox.
All that said, I don't really care about my choice in browser very much, but I'd rather support Mozilla over Google still. Especially since they're the only non-Chromium and v8 engine out there aside from Safari, which is also owned by a massive for profit company. I'd like to help support a more open web, even if it's just a little bit.