Cannot sign in to zotero forums from firefox

oldtimer

Hi,

Strange problem: From firefox (2.0.0.3, iceweasel, debian) I cannot sign
in to zotero: the username/password combination is processed for a while,
there is no error messagen, but the page still shows a link "sign in"-
No such problems with other sites.

Using opera, sign-in to zotero works without any difficulty.

Any suggestions what the cause could be ?
I disabled all firefox add-ons, but the problem persists.

Thanks !