With WebExtensions we introduce many more options to detect changes an extension makes to the browser. This can be used to surface cases the users should be aware of, or to inform users when they are interested in that information (to feel more in control of their extensions and themes). This is currently fairly high level and about to be further defined. It might include re-building parts of the add-on manager to accommodate for that information, integrate buts of it in about:preferences or other UI as well as creating new UI to surface relevant information in contexts where they are needed. (First example of that is a doorhanger notification after an extension changed the New Tab, to confirm if the user want that change. And the identify piece for extension provided tabs) Will start to collect ux related bugs under this one to better scope it.