Giving it five stars because it actually works in the new firefox versions. It's a bit awkward having to go to the addons page to make changes, be nice if there was a toolbar button for easy access but it seems as if web extensions are all doing this.

The addon itself does the job however. I particularly like being able to set unique agents for specific sites. This is coming in handy right for now for youtube since by using an IE11 string I'm automatically getting the old format back. I know this won't last but as long as it does I'll make use of it.