The only thing that kept me away all of these years is the lack of extensions and because I’m used to Chrome’s developer tools.
Firefox is the worst browser in literally every way except for the containers. Everything else feels hacked on compared to other browsers. Just compare Firefox’ reader mode to Safari. It’s night and day. Firefox’ feels hacked on.
As a developer I hate Safari, but as a user it’s everything a browser should be. With Translations coming in Big Sur it doesn’t have much to envy Chrome.
I use Chrome for Google apps. Gmail, GCal, etc.
I use Firefox for work and isolation. So I use containers to keep all my AWS logins/consoles separate, I use it for Github, I use it for my own internal apps and dev (and all the dev tools). If for some reason I need to do Facebook or Insta I do it in FF, and it's isolated into its own container.
Firefox is also my default browser, so if I click a link in another app, it'll open in a container in Firefox.
But yes, overall it is such an inferior browser, kept forcefully relevant by the iPhone alone.