If you use GreaseMonkey... Please read this..
If you use GreaseMonkey then please please please read Mark Pilgrims post on a very severe, hugely easily exploitable bug in GreaseMonkey that could potentially send ANY file in your local hard disk to ANY url, ANYWHERE.
For full details: Full details on GreaseMonkey exploit.http://mozdev.org/pipermail/greasemonkey/2005-July/004022.html
Please please uninstall GreaseMonkey until this is fixed, either that or remove all * targets and replace them with targets only to trusted websites.