Cookie-Editor от Moustachauve

Cookie-Editor is designed to have a simple to use interface that let you do most standard cookie operations. It is ideal for developing and testing web pages.

You can easily create, edit and delete a cookie for the current page that you are visiting.
There is also a handy button to mass delete all the cookies for the current page.
You can also Import and/or Export cookies.
Cookie-Editor fully support Firefox Containers.

The add-on is available also available on Firefox for Android for easy and convenient cookie manipulation on a mobile device.