Best in it's class. Lots of well thought out options so you configure exactly the way you want. Developer extremely responsive - issues resolved quickly. This isn't one of those extensions that rest on it's laurels and before you know it are showing their age. The entire Checker Plus series of addons are consistently evolving - the developer is always thinking about ways to improve them. The Checker Plus extensions were originally developed for the Chrome browser where they have been very popular for years. This developer took the time and effort to port his extensions early on in the Fx web-extension process. He didn't wait for Fx 57. Highly recommended.