That's a virus for ya!
Most probably you got a virus inside firefox, becoz the popup only shows when you open firefox. Still, this is just an educated guess and you still need to have complete scan on your sistem

Okey, I forget...
Try to look at your addon.
Go to Tools>Add-Ons

This post has been edited by minoru89: Nov 7 2008, 07:29 PM

Okey, I forgot...
Try to look at your addon.
Go to Tools>Add-Ons

This post has been edited by minoru89: Nov 7 2008, 07:30 PM

possible (not harmful) addons that might cause it.
or possible harmful addons

then it's back to the first thing.
Scan your firefox folders first, then if nothing found, do a quick scan..
This is something beyond help for me (over the internet)~

It might be best if you consult someone one-on-one
coz over internet nothing much can be achieved.

~~
last resort: Uninstall firrefox, delete anything related to firefox
eg. folders, temporary folders, registry(you shouldn't messing with this if you don't know)

then only install a clean firefox

This post has been edited by minoru89: Nov 7 2008, 07:53 PM

use your windows search
press F3 or find it in your start menu.

Too lazy to find it for you, it's diff with diff OS