I would've switched from FF to Opera a long time ago if not for one very awesome thing: on FF the history is kept not by alphabet but by the number of clicks. So when I type 'J' on the browser Juventuz.com links comes before Juventus.com ones.
I like the fact it starts instantly, even at first load, it takes less than a second to open on my PC. Opera takes 4-5 seconds on first load, and FF takes ages.
But the most important thing, Opera is the fastest at loading pages.