Local Storage Data = Firefox Offline Website Data. It does not clean it from the folder 'C:\Users\User\AppData\Roaming\Mozilla\Firefox\Profiles\user.default\storage\default.

If it did I'd give it 5 stars, so instead of 2 clicks, I go with 3 clicks with FF's built in history cleaner.

Does NOT remove all cookies, e.g., youtube-nocookie.com 64kb remains in Manage Data despitre multiple attempts to clear it.

This one actually works! I've tried several other similar add-ons, and none of them worked. But this one does.
If it had the option to clear everything when I close Firefox, then I'd give it five stars.

It's not really worth using as long as it cannot clear data from YouTube, which is owned by Google, which is the largest data gathering company, and the one we'd most want to remove tracks from. Perhaps in the future this will be fixed and I'll give it another try and update this review. Good concept and a good start, but so far it's still incomplete.