@Codeawayhaley
You can install CookieAutoDelete that will manage your cookie settings, and set it go delete cookies after specified period of time. You can test it out for a month duration
@Codeawayhaley Yes, I understand now what you want, but nothing crosses my mind how to solve that.
@nikolal I don't want to delete them, I'm happy to leave it up to firefox's garbage collection, I want a way to lock a cookies expire time and prevent that site editing it back to the original expirery time.
once a cookie expires firefox won't send it therefore the site can't know of it nor edit it, but it won't necessarily be deleted right away unless necessary.