CT's answer above may seem not particularly helpful to you . . .
especially since you just registered here to ask this question.
But you really should have given us more information as to what you are looking for, etc.
However, I'll give you my opinion:
Most of us who participate here are just other Mac users, asking questions and sharing solutions. So, with that in mind:
Safari is an Apple product. Very easy to use in theMac/Apple environment.
Firefox is also excellent. It is my second browser. It's not Apple, and it works on both Apple & PCs.
There are sites that are not compliant with the web excellence standards, that Firefox will read, despite the lack of good programming.
That's the difference, really.
The best thing is to have both.
I started in Mac after using Firefox due to its specific cookie storage handling. I never learned how duplicate in Safari before giving up on it.
But others have to comment on how Safari duplicates that behavior.