hello Talbergotti, you might have an external "tune-up" or clean-up tool installed on your computer that is interfering with the cookie management in firefox.

Maybe. Which program could it be? Doesn't happen in IE10.

there are various software programs like CCleaner, Advanced WindowsCare, and many others more that would offer such functionality...

Or maybe one of the three anti-virus applications which show in your extensions; 2 of which are active. Avast, Norton, and ZoneAlarm show up in your extensions. You really should uninstall old anti-virus applications when change to a new av program.

Norton has be uninstalled. Don't know why it keeps showing up. ZoneAlarm AV is not activated. CCleaner is set to not delete cookies. Again, this only happens in FF and not in IE10.

for firefox it won't make a difference if you restart the browser immediately after you've closed it or perform a restart of your computer in between. something external must be interfering here...

Like what?

like the tools already mentioned above. ccleaner certainly has the functionality to run in the background after startup of your pc and perform clean-up tasks. i cannot look onto your computer and see what (if any) similar programs are there - you'd have to go into the settings of such programs to make sure that they are not set up to automatically delete any part of the history or cookies in firefox or uninstall them from your computer...

Which security software (firewall, anti-virus) do you have?

Some security software has virtualization or sandbox features that may cause problems by protecting and restoring files in the Firefox profile folder possibility after a reboot.

ZoneAlarm and Avast.