Rated 5 out of 5 stars

Been using it for ages and hasn't let me down once.
I just want to take this opportunity to ask the developer if he will be upgrading this add-on into a WebExtension.

This review is for a previous version of the add-on (6.0.1). 

Yes, there will be a WebExtension version in a few weeks / months. I don't know a release date but the WebExtension will be available before the release of Firefox 57.