IME the features are often mostly there same but there are small implementation differences/bugs at least in the newer APIs. Firefox is no more buggy (often less), but it's easier to code for one set of bugs. Safari is by far the worst.

I use Firefox for all my browsing, but do web app development with and for Chromium. I'd gladly do it for Firefox, but people, especially users, suck and sometimes one has to accept this.

Glad to see no time is wasted for Safari/iOS support. It's a huge waste of time and people using Apple devices are to blame.