I see entries in our logs that suggest that this is a problem on our end. I'll investigate.
Looks like out of 2000 distinct IPs hitting that forum in the span of the few hours I'm looking at, you're one of 3 having this issue.
Firefox 3.6.9 introduced some security changes which have caused issues with all in-browser WYSIWYG editors. We've been investigating workarounds for several days, and are aiming to include a solution in the upcoming release.
Thank you for the quick response! Definitely gives us somewhere to start.
Do you have any sort of translation software/browser plugins installed? We've seen odd interaction between the post editor and certain plugins in the past.