Until now, very few developers had access to submit an extension for the new Microsoft Edge browser. Microsoft is changing this situation today by opening up the Edge extension platform to all developers. Any developer can now submit their extensions in the Partner Center Developer Dashboard. Since the new Edge browser is based on Chromium, most of the Chromium extensions will work without any change. Microsoft is also offering some Edge-specific APIs, developers can learn more about it here.
Microsoft today also announced that they no longer accept new submissions for Microsoft Edge Legacy (EdgeHTML-based) extensions from today. However, developers can continue to submit updates for their existing extensions.
In order to improve the transition experience from old Edge browser to the new Edge browser, Microsoft will migrate users’ extensions from the current version of Edge when they update to the new Microsoft Edge from January 15th. Microsoft will do this migration only if extensions are already available on the Microsoft Edge Addons store at the time of switching to the new browser.
If you are a extension developer, you can learn more from the source link below.