Rated 5 out of 5 stars

Strength:
• Open source. If you are not familiar with "open source", it means this app is more secure. Because its code is publicly available for review and contributions on GitHub at https://github.com/JustOff/cookies-exterminator
• Attractive GNU General Public License version 3. This means the software code of this add-on app is owned and supported by a friendly not-for-profit community. Instead of a for-profit corporation. And more secure because its full code is publicly available for review.
• Easy to use. Using the button in the browser toolbar.
• Whitelist cookies. Very easy. Two clicks to whitelist a website.
• Frequent add-on updates
• “Active mode” allow you to optionally automatically delete cookies after a set delay
• Export or import all or only selected cookies
• Backup or restore the add-on configuration
• Edit cookies
• Well documented
• Works with Firefox 52 or more recent
• Many many more features

Challenge:
• When "Active move" is disabled, the toolbar icon design color is small and hard to see on large screens. It is a tiny dot inside a circle. It does work :) But it is just hard to see :( I contributed a suggestion with this ticket at https://github.com/JustOff/cookies-exterminator/issues/8

• The add-on preferences can not be open from the toolbar icon. I suggest to add this feature. Meanwhile the preferences are accessible at about:addons

• The handy “Active mode” allow you to optionally automatically delete cookies after a set delay. But the delay range from 1 second to 10 minutes. It would be useful to be able to set a longer. I suggest an unlimited delay?

• Not compatible with Firefox 57+. Due to challenges not yet resolved with Mozilla does not yet provide all the necessary APIs that could allow to migrate this add-on to WebExtensions.

Using:
• Add-on 2.9.2
• Firefox 52.8.0 (64-bit)
• Debian 8 Jessie 64-bit
• GNOME 3.14.1

This review is for a previous version of the add-on (2.9.2). 

Thanks for your feedback. Let's use GitHub issues to discuss the details.