Due to a critical security flaw, Mozilla Update for Firefox versions prior to 1.04 have been shutdown.
There was a flaw in the IconURL parameter(in version prior to 1.04), which could allow an attacker to gain access to your computer.
A Story on the bugs in Firefox 1.03, and earlier. http://news.yahoo.com/s/nf/34797
To install newer themes, or extensions via Mozilla Update, you will have to upgrade to Firefox 1.04.
You can then access Themes and Extensions for Prior versions of Firefox, if you need to.
Is 1.04 out yet? EDIT: Yup - http://www.mozilla.org/products/firefox/start/ Anyway - I still trust Firefox over IE. No matter how many spyware removal programs I run, something always lodges itself in unreachable places and changes my homepage. I just don't bother with IE. At all. I used to only use it for Windows Update and Hotmail (M$ specifically disable some features for non-IE) but now with the extensions available for Firefox they are no longer issues.
Yeah 1.04 is out, for me, it just automatically updated my version.