Microsoft's addition of extension support for the preview version of Microsoft Edge on Windows 10 seems to be gaining steam among third-parties. A popular open source browser extension, Turn Off the Lights, have released the first version for Microsoft Edge.
The app has a simple but useful feature. It can darken the background of a monitor or display when a person wants to watch a video in a web browser. The fact that the team has ported the extension to Microsoft Edge could be evidence that we could see even more such efforts in the future.
Bear in mind this release is just for the version of Microsoft Edge that's included in the latest preview version of Windows 10, build 14291. Also, the extension must be downloaded and then side-loaded onto the browser to work. Microsoft has already said it plans to offer more direct download support via the Windows Store, in the future.