I feel compelled to point out that Opera had these Firefox "innovations" long before they showed up in Firefox. The things popular Firefox plugins do are already built into Opera, for the most part.
about:config is one thing I hate about Firefox. Why aren't most of those settings available to ordinary mortals in a menu or human readable form, as they are in Opera? It disgusts me that I have to go into about:config to make the backspace key work like in does in most browsers. And there's nothing to help you out, nothing that explains the obscure settings.
I don't dislike Firefox and I do use it sometimes. But Opera is my main browser in all operating systems and has been since Windows 3.1 days.
Welp, I found a rendering option that requires about:config in Opera 11.6x.
Opera hides some options, too.