I've tested it using the same method we use for Notepad and it doesn't really work. It sort of works but causes other problems, so I don't think this is possible.

Sorry!

There is actually a program that works well for browsers called BrowserChooser2 - It allows you to make it the default HTML (and other protocols) handler, and then lists the browsers that you have installed to pick which one to load in.

Unfortunately, the website https://browserchooser2.com/ is currently down (as of today, 17 Jan 2019), but I do have a local copy of hte BC2 last release from Feb 2018, BC2 Release 2 (Version 2.0.4.38373). I've contacted the dev via Twitter to ask if he knew the website was down.

His BitBucket site https://bitbucket.org/gmyx/browserchooser2/downloads/ Has the previous release, but it is not nearly as friendly with Windows 10 as the R2 release.

I have not obtained any permission from him to re-distribute his file, so I cannot (currnetly) attach it here, but if I hear something back from him otherwise, I'll post back.

I stumbled upon EdgeDeflector, which seems to do the work for me. It's designed to redirect calls from Cortana.

Thanks for this.

Since BrowserChooser2 allows for defined protocol support (including adding your own) I'm going to delve into the various 'X-edge' protocols and see if I can get BC2 to take control of them - if so, that will be a huge win for BC2 as well.