DRI: antlam (UX) add-ons will be signed by Mozilla in order to further protect our users from only being able to install Mozilla-signed add-ons to Firefox, whether this is desktop or mobile. UI/UX is needed before we enabled the support for signed add-ons to inform the user why an add-on wasn't installed if it wasn't signed, if a currently-installed add-on isn't signed and therefore will no longer work, etc. Actual support for signed add-ons is already ready, but is currently switched off. Turning it on is a configuration change which needs to be tracked closely in order to coordinate with this feature's release. NB - target implementation on desktop is Fx 40, therefore mobile will be one release behind.