On my parents' Windows 7 PC, Firefox always tells my mum that it's not the default browser (giving her the option to make it so) and then when closing, it pins itself to the taskbar. I've checked and according to Default Programs Firefox 'has all its defaults'. I've tried making IE the default and then returning it to Firefox but the problem still occurs. The PC has no other browsers on it. Clicklinks in Thunderbird cause Firefox to open, not IE so it seems as if it is actually the default. When closing Firefox it always pins itself to the taskbar. I can unpin it and still, when it closes, it is there. From Googling, I have a suspicion that the pinning happens when setting Firefox to be the default. I also have a suspicion that something is wrong with the setup for the default for the HTTP protocol as it doesn't exist as a protocol in Control Panel\Programs\Default Programs\Set Associations