I've been developing a Javascript intensive bookmarklet for the past month or so. It works on FF, Chrome, Safari, even IE6. But on Opera, I cannot figure out why it behaves so glitchy. Sometimes it works, sometimes it doesn't, but it never, ever shows me any errors. Maybe this has to do with the fact that it caches things even when you tell it not to. In addition to that, AFAIK there's no way to deselect text (without breaking other things), which makes developing drag and drop pretty much impossible on it. It's "developer tools" show you a big list of "errors" which are mostly it knit-picking various CSS properties things that it doesn't support, like rounded corners for example.
Perhaps I'm wrong. Maybe my code is getting run perfectly, but it's just happening so blazingly fast that it doesn't affect anything at all. In which case, I'd still give Opera the big "fuck you" that I'm feeling after writing this.
I've also found that Opera is annoying about caching stuff that it thinks is local (192.168.. or file:///). It aggressively caches, and is reluctant to reload, certain pages on our Django site on our local dev machines - but the problem doesn't repro on production. I don't know if it's a bug, or a setting I can turn off, but if I work it out I'll let you know.