I also had that yesterday, it came back after a refresh, so I assumed that there was a small change somewhere that was incompatible with something in the cache.
But if it continues to happen maybe there is something else; I'll report it.

I'm having some bugs today, sometimes the only thing that appears at the forum index is the private messages section, other times I don't get the menu at the top (to click back to the main site).

Not a big issue, as I usually get the normal forum view after a refresh or two.

It has been fixed

OK I'll report the bug

Preview no longer works at all, this time. Once again, tested on several web browsers, with or without anti-ad / anti-cookies add-ons.

Looks like the Forum format bug has been fixed.

I still use the IE browser

I didn't ask, but most likely CSS indeed

Thanks! Corrected, indeed.
Any information about what the problem was?

Indeed... I'll forward the info

Seems to be a bug with the top of the preview window:
- it no longer displays the left "Preview" writing directly: it have to be selected to be seen (Ok, I don't really miss it );
- there is no closing cross for that window. It must be there, as clicking in the right top corner close the window...

Repeatable with Firefox (Gecko) with or without ad- and cookies blockers and Midori (WebKit). Please don't ask me to install Chromium nor Konqueror for further tests. Furthermore, Chrome is "persona non-grata" on my computer, and IE4Linux no longer works (and who still uses IE???)
I agree to test more with Dillo or Lynx

Could it be a Css problem? This message is just for feedback, as this bug doesn't really bother for writing.