People on the Windows Insider program who have the current preview version of Windows 10 installed can now download a select number of Microsoft Edge extensions from the Windows Store. However, it appears those extensions cannot be used yet in the browser.
Microsoft added support for extensions to Edge in a recent preview build of Windows 10. However, it stated that those extensions have to be side-loaded to Edge in order to work with the browser. Now with some extensions such as Pin It Button from Pinterest showing up in Windows Store listing, it should not be long before Windows 10 Insiders will be able to directly download them without the need for side-loading.
Microsoft plans to enable full support for extensions in Microsoft Edge as part of its big Windows 10 Anniversary Update, which will be released for free later this summer. Windows Insiders are getting an early look now and we bet the next release for PC will let these Store installations work as they should.