Have you ever posted on any of the MSDN forums? Did you think the editor was adequate? If not, I have some good news for you. Our team was recently asked to write an improved rich text editor for MSDN forums posts. It will support IE and Firefox browsers. We don't know yet when it will get released because we are contributing it to another team and they will control the actual release. But, when it is released, the new editor should provide an improved experience on both Firefox and IE but I think Firefox users will see the biggest change. We're testing it on both Firefox 1.5 and 2.0 so the most common Firefox versions should behave pretty well.
After it is released, feel free to add bug reports/repros or feature requests as comments here. We need to hear from you to improve it!