During my dial-up days, Opera has a feature of loading cached images / no images / images. Since in those days, I mostly used to check by mail and very little surfing, Opera made things easy. FF was not born. I am using Opera since Opera 6
It is innovative and many innovations are taken by others browsers from Opera. Opera used to strickly follow web standards as against IE 5. (I do not know how they follow standards today). So many pages did not load properly in Opera. It's innovative features like first tabbed interface, notes, speed dial , trash can, opera sync made Opera my main browser.
However, as said by other minters
, Opera does have some compatibility, not because of bugs, but since many web devs do not keep opera and standards (strickly) in mind while designing websites.
Recently, after introducing extensions, Opera cold start (first start after OS booting) has increased a lot and it freezes seconds after starting for few seconds in XP and not Linux (atleast Ubuntu based). Again it has closing issues, reasons unknown, since 10.10. A Process keeps running in back ground even after opera is closed and it will not allow Opera to launch, since it is already running. So I have to end process from task manager.
Refer the link in opera forumProblems when closing down Opera 11.50
6 week release cycle has not helped FF.