I'm sure you're right. Viruses were being written for IE because that's the one that everybody has been using. Now that Firefox is popular, I'm sure the hackers are already turning their attention to it.
Viruses can also more easily attack IE than Mozilla or Opera because of the difference in how they implement their security models. IE's support for ActiveX controls makes it very easy to write a bonafide virus and drop it into a web page.
umm people have written viruses for specific cell phones with an install base of less than 100K....