depends on your target audience.. I mean, some universities have firefox on them, right? only (i think) the third world countries have IE6 for default. (I know, I see them) I don't know about other countries, though. But I'm pretty sure still a large chunk of the population still use IE6 by default.
If you think it's really necessary ( I think so), go ahead. I don't see any problem in it. ('cuz I'm inexperienced in software development and such.. XD)
