It's just a bundled extension inside Firefox. You can't uninstall bundled extensions, and you can bundle yours in your custom Firefox installation if you want.
Did a similar thing for a project, rolled out customer's own Firefox extensions (for office workflow) to employee desktops. Extensions were bundled because the employers sometimes uninstall them and freak out because they can't work anymore.
Pocket is not an extension - it's built in by default and cannot be removed (only disabled).