LeechBlock NG is a masterpiece on the desktop, but be careful if you are using it on Android to fight a serious scrolling addiction.
​The "Advanced Options" that allow you to block about:addons or about:config simply do not work on the Firefox Mobile app. On Android, the Add-on manager is part of the browser's native UI, not a web page that the extension can "hook" into. This means there is no way to prevent yourself from simply clicking the three dots and deactivating or deleting the extension whenever you feel a craving for YouTube or Instagram.
​If you are like me and looking for a "hard lock" that you can't bypass by just deleting the addon, this isn't it for mobile. On a PC, you can use the password/USB-stick trick to lock yourself out of the settings, but on a Samsung or any other Android phone, the browser's own menu provides a permanent backdoor.
​Pros: Same great filtering engine as desktop.
Cons: Cannot prevent deactivation/uninstallation on mobile due to Android Firefox limitations.