I'll throw in my 2c here.
Been using Opera since 2.1 in 1998.
There are things (some of them mentioned in this thread) that do frustrate me, but none of them even remotely make me consider switching to FF or Chrome
So then I need use FF again and pretty soon I'm ready to shout in frustration.
I use FF only because of DownThemAll and that only because of it's capability to rename PDFs using the link's text label instead of the filename.
Opera
My favorite anecdote (not that it means all that much these days).
On dial-up (1998), opened IE , typed in url, pressed enter and waited.
Started Opera, typed in url, pressed enter, got full page.
Switched to IE - still waiting for full page to load.
This on many sites, not just one.
Opera - still making other browsers feel glacial.