I installed Flagfox many years ago and use it since that day because Flagfox is really one of my very essential add-ons. I'm very happy to see that the developer has ported it to a web extension for Firefox >57 just recently. Many, many thanks! The icons look a bit different now (as explained by the developer and I can easily live with it), but all the functionality I need and love is still there which is most important for me. Fully worth to deserve 5 stars!