Microsoft had originally planned to release extensions support for its Edge browser in the recent major Windows 10 update. Those plans hit some delays, and the official release is now expected in early 2016. Thanks to an accidental preview site going early yesterday, it appears that Microsoft is very close to previewing browser extensions for Edge.
Twitter user WalkingCat discovered Microsoft's mistake, revealing a developer site announcing extensions support for Edge. It appears that Microsoft's early preview will allow Windows 10 testers to manually download and install extensions, with documentation to enable developers to create their own. Reddit and Pinterest extensions appear to be the only test extensions ready for the initial preview. Microsoft is planning to include extensions in the Window Store once the support is fully tested, and Chrome developers will be able to easily port their extensions across.