Firefox performances have been good for so many years that I can't remember when it was the last time that I felt it to be slow. I only remember that Chrome used to be faster than FF (mainly the JS engine) and then it wasn't. Maybe it loses every single benchmark, I didn't check, but it is fast enough to be my primary browser, the one I use when I work as web developer and also when I'm not working. I run FF on a 2014 Debian laptop. Windows and Mac, who knows.

About compatibility, there are some odd sites that use a Chrome only API or something that FF didn't implement. They are really rare but people that must use one of them to do their job don't have a choice.

Then I intentionally break every single site by using privacy add-ons like uBO, uMatrix, PrivacyBadger etc so sometimes I have to play with them and find a configuration that lets me use a site. In the case of uMatrix it usually means finding the minimum set of scripts that enables enough functionality leaving out all the 3rd party tracking and then saving it. When it's too complicated and I will not use that site again but I must use it, I either disable every add-on on that site or I run Chrome.

Finally, I run integration tests with a headless Chrome, but I develop with FF. If it works with FF it works with Chrome and Safari too.

BTW, I use FF on Android as my primary browser too.