Browser extensions were absent from Windows 10’s Edge as Microsoft and developers got things right and optimized to be used with the browser. Build 14291 features extensions support with Edge for testing purposes.
The feature will let users try out Microsoft Translator, Mouse Gestures, and Reddit. Not a large or diverse amount of extensions—or even ones that everyone will want to use—but that’s what Windows 10 users are getting if they use Edge regularly.
One thing to note is that these particular extensions can be installed in Chrome. Likewise, porting of extensions made for Chrome can be done and is encouraged to give Edge a good amount of apps to choose from as opposed to attempting to sell developers on making browser-specific versions of their extensions.
Edge is a new browser and will need to show itself functional with a lot of those extensions as testers try them out. If this testing period looks good, extensions could be available on Edge much sooner rather than later for all users.