These are the main reasons I don't use Firefox regularly:
1. Terrible scroll wheel support (as with many Carbon programs), and poor scrolling performance from the keyboard.
2. Completely non-standard interface elements. (Not at all Mac-like.) I feel like I have to wrestle with it to get it to do what I want.
3. It's just never seemed like a finished product.
Camino has perfect, standard scroll wheel support, and good scrolling performance all across the board. It also has a completely Mac-like interface, which is much more responsive than Firefox's hackish design. And while each version of Camino does have its issues, it still feels solid to me.
But this is all coming from a Safari user. These are the main reasons I don't use Camino regularly:
1. Poor feature set. It has filters and a popup blocker, but they just aren't very good.
2. There are virtually no extensions available for it, so there's no way to fix its poor feature set.
The truth is, most browsers have poor feature sets by my standards. In Firefox, I rely on Adblock, among others. In Safari, I rely on PithHelmet. The only browser I consider really usable without third-party help is iCab (too bad its rendering engine is slow and outdated). The problem is that Camino doesn't have that third-party help that Firefox and Safari do.
The reasons I DO use Safari:
1. It's Mac-like, even more than Camino (for example, Safari gives OS X's standard spell checking in text fields like this one, whereas for some reason Camino doesn't).
2. It lets me specify a custom CSS file (I still can't believe Firefox doesn't have this feature, but damned if I can find it!)
3. Third parties beef it up with extensions like PithHelmet.
4. It has a better tabs system than Firefox (Camino's is good, too).
Basically, Camino is too weak for my liking, and Firefox is too frustrating and un-Mac-like. Safari wins by default. Thank goodness for PithHelmet.
Oh, how I wish I could go back to using iCab all the time.....