No, there aren't. Malware is primarily created for profit these days, not just to cause trouble. Opera has a marketshare of under 1%. It is meaningless to target.
And Firefox fanatics should be careful what they wish for.
Firefox has an inherently unsafe design, where absolutely everything (the browser, extensions, and plugins) run with the full privileges the user has and have full access to the machine.
This is in contrast to recent versions of IE where there is heavy separation and sandboxing. As an example, ActiveX objects no longer have full access to the machine, they only have access to a highly restricted environment where most things (including the file system) is virtualized so that they can't infect the rest of Windows with any malware. Quite a lot of Firefox users have a habit of blindly installing any extensions they come across, oblivious to the fact that they can infact include any code. It's a recipe for disaster.
It reminds me a little of Mac fanatics that insist on ignoring fundamental security shortcomings in OS X because no one have exploited them yet. That is not the right way to think. You want to foundation to be as safe as possible so that you don't risk running into problems in the future.