If you've upgraded to Firefox 3.5,
and you had VirtualDJ Radio before...
For sure you've seen the toolbar doesn't works properly.
The way to solve this problem is to uninstall this add-on on Firefox.
And re-install it again, so just follow this few steps:
1. Open Firefox Add-Ons, under the TOOLS menu
2. Select "virtuadj_radio Toolbar"
3. Click the uninstall button.
This will make you restart Firefox
4. Once Firefox is opened again, install a new fresh version of the Toolbar
http://virtualdjradio.ourtoolbar.com/
This will make you restart Firefox (again).
Hope this helps.
(Feedback here will be thanked)