I am using the latest version of Firefox (57.0.4) to test my IT Hit WebDav server implementation. When I attempt to open a file other than MS Office I expect to be prompted to install the protocol installer. Rather than being prompted I get a dialog that says I need to install something from the Windows App Store. I see the same behavior with Edge.
Both Chrome and IE are behaving as expected. It appears to be supported by Firefox.
I also tested using the Ajax browser on Firefox and it fails as well.
Thanks!
The issue with Firefox is fixed in the IT Hit WebDAV Ajax Library v5.
You can find a detailed answer about why the protocol app is not detected and the callback is called here.