Sorry if this has been posted before, just a little tip for people who struggle to get their cashback sites tracked.
I use VMPlayer(used to run virtual PCs on a PC) with a ready made VM Machine called Browser Appliance. You can set this(and I think it is set by default) to never save any changes - which means no cookies/activex controls/etc etc are ever stored, and each time you run it, it is like a fresh install of Firefox. I always use this to track Quidco to prevent cookies getting in the way, and I have always had my transactions tracked.
Browser Appliance: http://www.vmware.com/appliances/directory/browserapp.html
List of instructions is here: http://www.spywareinfo.com/articles/vmware/baintro.php
Hope this helps someone :)