Delete cookies in Firefox after specific interval of time

By default firefox can be set to delete cookies after a set time, but it can only be set by number of days, if that is of use to you then you can do this.

Go to about:config

Set network.cookie.lifetimePolicyto to 3

and

network.cookie.lifetime.days to 1

You could also set

network.cookie.lifetimePolicy to 2 if you only want them to last the browser session

If you install and setup CCleaner to erase cookies you could also run it on a scheduled task with

CCleaner.exe /AUTO