"Opera and Chrome are both slower for me than Firefox, unfortunately. Opera is also slower in terms of interface."
Firefox certainly have compelling features on its own, such as a very large library of good add-ons, ActiveX support and so on. That said the one thing it isn't, in comparison to Opera and Chrome, is faster.
I tried Firefox and while it's not a bad browser I found it to be too slow and unstable, presumably mostly due to the add-on support, in comparison to Opera.
When Chrome came out of beta I switched over pretty much instantly though, as my main gripes with Opera were the cluttered UI and 'everything-and-the-kitchen-sink' approach to functionality inclusion.
On top of that Chrome were even faster too.
No dig against Firefox then but it's certainly not faster than Chrome or Opera for the vast majority of users.