If you want to customize your Firefox there are lot of addons available to fulfill your needs. Unfortunately, you can’t install the experimental addons to your Firefox without Mozilla account as it may cause problems to well running browser. Still you want to install the addon you have to register for an account with Mozilla and sign in before downloading and installing these plugins. Nevertheless, now this problem is solved therefore you can install the experimental addon without signing up for an account.
In order to use this addons you have to check a box that represents you’re sure you want to install an experimental add-on. If the box is left unchecked, the green “Add to Firefox” button will remain white and un-clickable.