We had a sharepoint-based wiki at one point. We salvaged as much content as we could and moved it to mediawiki, which actually worked* . Half our office was convinced sharepoint was deliberately designed for incompatibility with firefox. (Is there such thing as a "cygwin shop", by the way?)
The thing that makes Sharepoint completely unusable for me is that all the links are of the javascript() variety, so quickly opening pages in tabs is functionally impossible.
It would be nice if browsers could handle middle clicks a little more gracefully in this situation.
Pretty sure it's just the normal "works only with IE" stance of most Microsoft stuff. I did some testing with Firefox and Sharepoint for work to see what doesn't work and it's fairly extensive. The worst issue stopping non-techies is that the rich text editor for textareas doesn't work in FF, you have to type in raw HTML. Pretty much a showstopper. This was SP 2007 btw, not sure if 2010 is any better. The blog and wiki features in SP2007 felt tacked on and incomplete to me anyway.
* Usemod is also quite good, but less stylish.