I hate having to login to certain sites over and over, especially if I've enabled two-factor authentication on my account and can't be bothered opening Authy on my phone every time, so I like to keep my cookies for as long as possible. However, an overabundance of cookies in your Firefox profile directory is both a privacy and a performance nightmare, and it's often necessary to clear your cookies in order to correct certain browsing issues, which means re-logging into all of your usual haunts.

With Cookie AutoDelete, you can choose which cookies you want to keep, and it will automatically (or manually, if you like) delete all of the other cookies that you haven't specifically protected. It protects cookies by whitelisting URLs whose cookies you want to keep, and you can choose only to protect certain types of cookie from specific sub-domains. You can also specify how often and under what circumstances you wish the add-on to silently clear unprotected cookies in the background. If you like, you can have the add-on notify you every time it does this. The toolbar icon shows the number of cookies the current URL is generating and the icon is also colour-coded to show whether or not cookies are protected on the current URL (blue for "yes", red for "no"). The convenience and usability of Cookie AutoDelete is very high.

There's not much in the way of competition for this add-on, it's simply the best of its kind that I've used. I'm including in that comparison those cookie-management add-ons which are exclusive to other browsers like Chrome.