Roughly two months ago. Windows and Android. A few things that make it very tough for me:
Autofilling. Chrome is just so much better and it's something I have to do a lot for my business. I'm always buying random parts from random places and a lot of them don't have the best-designed forms. Chrome handles them much better. There's just so much friction removed when you don't have to type all your info, especially on a phone, or pull out your credit card. I now have my credit card number memorized thanks to having to do so so much with Firefox. I had the same credit card for years, but with chrome I so rarely had to actually pull it out that I couldn't have told you more than the last 4 digits.
Chrome's built in password management is just better at picking up logins and passwords too when forms aren't designed really well.
I get a lot more performance issues with Firefox. I have to force close it sometimes. Never happened with chrome. It's not super frequent by any means but it happens.
Lot of websites don't work in Firefox and I have to open them in Chrome which is likely not Firefox's fault the majority of the time, just developers not testing in Firefox, but still quite annoying to me.