I was having the same problem while developing my own website. While it was resident locally, resources opened as file//
. For pages from the internet, including my own loaded as http://
, the F12 Developer did use Edge as default, but not while they were loaded into IE11 from local files.
After following the suggestions above, I unchecked the box for "Display intranet Sites in Compatibility View".
That did the trick without adding any extra coding to my web page, or adding a multitude of pages to populate the list. Now all local files open in Edge document mode with F12.
So if you are referring to using F12 for locally hosted files, this may help.