This extension completely broke my Firefox, every single website stopped working after installing this extension, I can't even browse any website because nothing will load properly.

Edit: This extension broke my whole profile, not just the browser, I had to completely uninstall Firefox and prevent sync from automatically downloading my extensions (sync wasn't downloading this extension at all), after that, I had to manually download every extension I had, as well as rewrite all of my chrome.css and content.css code. I have no idea how this extension managed to break my profile but it did.

Why users have to use this when there is "Delete cookies and site data when Firefox is closed?"

Firefox can block, allow, allow session per website in Settings, Privacy & Security, Manage Exceptions…

Please add a feature to clean cookies periodically, so that when open many pages on a website for a long time won't be collected too much

I'd like to love this in principle, as it would be far superior to Firefox's built-in cookie management options. In practice, the add-on is selective and unreliable in the cookies it deletes. I've followed some of the recommended troubleshooting via the FAQ, including add-on reset and turning off other cookie related add-ons, but the end result is still not good. As I'm not willing to sink more hours into community troubleshooting, I have to uninstall this disappointed.

My lesson here is that if for whatever reason its not working, and cookies are not being deleted, as per browser data in the settings, click on RESET TO DEFAULT button for the extension. That seems to correct everything....although I still cant figure out why for the life of me it wont remove the two domains fuckme.com and fuckthem.com . I think its because if page doesnt display, then cookies are installed, yet browser still indicates that a cookie has been saved...hmm....

Use Firefox forget instead.
You should restart Firefox every time you delete cookies.
Private windows? nope. deletes all cookies from Firefox entirely!