It’s been more than a year since the Windows 10 Anniversary Update was released and Microsoft Edge got extensions support. To date, there are only 60+ Edge extensions available at the Windows Store, which is very less compared to the number of extensions available for mainstream browsers like Chrome or Firefox. Also, there are non-Store extensions that you can side-load into Edge.
Note: Information in this article does not apply to the new Microsoft Edge (Chromium). It’s applicable to the old Microsoft Edge browser only.