To be honest I've used IE forever. I tried firefox out, but just didn't like the way things were setup (used to IE I guess). IE and firefox do display some websites differently, however I don't know if that would be causing the smiley errors. If you write down 3 question marks you get this image

. The same thing could happen for other smileys.
There are obviously some issues that they are still working through (including proofreading).

firefox download page:
http://www.mozilla.com/en-US/products/download.html?product=firefox-2.0.0.6&os=win&lang=en-US