Microsoft recently announced the availability of Extension Support for Edge Browser on Windows 10 PC. This is available only for insiders build 1429. Being the popular OS on the desktop, and with new Browser on board, the first interest comes from Turn of the Lights. Its a popular extension which allows you to watch videos in complete focus with everything else dimmed down.
While Microsoft has promised to get more extension through the Windows 10 Store, as of now these extension from third parties need to be side loaded using the Developers mode. Hopefully in near feature we will see extension support for Edge in Windows 10 Mobile, but thats little far fetched as of now.
Microsoft is also working on a tool that will be able to convert the Extensions on Chrome to Edge. In fact few developers already have found a way, but then its not sure if they work exactly as needed.
Download the extension from here