The only thing I’ve done with Edge is play with it for a few minutes, then uninstall it. 🙂
There’s probably an option setting that determines how the browser handles file extensions. If you can find it, set the .gem extension directly to GemCad. This is convenient because you can view the file in GemCad, then choose to save it wherever you want from GemCad itself.
The other thing you probably want to do is set Windows to open .gem files with GemCad (or Gem Cut Studio, if you have it). If you haven’t done this before, you can find instructions on line, such as how-to-reset-file-associations-in-windows-10
No guarantees, since I don’t know much about Edge.