My understanding is that when the firefox 57 was released (I believe that was the version that dropped the old XUL add-on model) they did do some work to allow

My understanding is that when the firefox 57 was released (I believe that was the version that dropped the old XUL add-on model) they did do some work to allow the add-on developer to port it to the new model. Why exactly they still haven't implemented an easy way to hide the redundant top tab bar I can't explain though!