I still say that the "Get Firefox" campaign with the annoying message being thrown in my face on every page view is so 1999. It's your site though, so ultimately your choice. I just thought I'd chime in with a differing view.

If you'd like people to use Opera, then please feel free to promote it. I personally don't like Opera. The interface feels "heavy" and foreign to me. Firefox seems lighter and quicker. That's not measured results, just my own observation.

I think people promote Firefox over Opera based on preference rather than merits. Opera may have had some features first, or it may implement said features better, but it hasn't won us over yet. Whatever the case, both browsers beat Internet Explorer by light years, and I think you'd agree that more people using either option over IE would be better.

Opera still lacks a sufficient market share, at least in the arenas I operate in. It's about "good enough", not perfect. And while I'm a fan of competition, I'm not a fan of intentionally promoting the further fragmentation of the browserspace. Firefox has momentum that I don't see from Opera, and it's already more relevant to me, so I'm going to promote it over Opera, since they're both "good enough" in general.

I happen to particularly disdain the lack of support of attribute selectors in browsers, so that's the feature that I'm picking on. It should be relatively trivial to mod the CSS to pick on whichever feature happens to be your hot button issue.

I would disagree. I don't care what browser you use, as long as it's good enough. If you're not using such a browser, I'm going to point you at Firefox, but if you use something else that works right (Opera, Safari, etc.) that's fine with me.

And at the same time, you'll find that my site works just as well in "bad" browsers as good. You'll lose some of the eye candy, but the core design is still sound.

(And Fiferfox still isn't supporting inline-block! That really sucks!)

No browser is immune from bugs, quirky interpretations of the specs, browser-specific extensions to established standards, crappy support for technology xyz, etc, Firefox included.