A peculiar behaviour concerning div layout

I have not found something similar to this…or maybe i did not see it. Anyways, i have a normal, 3-column layout made of divs. It works smooth. The right sidebar though, has a tendency to roll down (only vertically) at the same level with the end of the content div, for no apparent reason. See for yourself:

[url]http://www.partidulconservator.ro[/url]

This behaviour is only noted on Mozilla, IE works fine (that’s smthgn new). And a refresh clears the problem sometimes, and sometimes not.(so, if you don’t see the error, please hit f5 several times or try navigating the left menu, especially the 2nd and 3rd items) I’d probably made a mistake. I cannot see it, though.

Please, anyone, heeelp!?

Also in #CSS _↴