You'll still need to use Chrome from time to time. You can even change the user agent of Chrome to Firefox to make sites see Firefox anyway.
Really? I've only used Firefox for over 5 years now, on Mac, Linux and Android. I don't need extensions to change my user agent either.
No? Unless you're a web dev and need to test under chrome, maybe. I have chrome on none of my personal devices.
When done site doesn’t work for some reason I go and use some other site. I’ve yet to encounter an essential chrome-only site.
That may or may not be an option.