[stonesweep]

Each DE can have slightly different paths, but in general find the file mimeapps.list. It's typically looked for in the traditional manner of /etc/, /usr/share/ and /usr/local/share/ and $HOME to find global, local and personal configurations. In your $HOME it's usually something like this:

    ~/.local/share/applications/mimeapps.list
    ~/.config/mimeapps.list

In here you find the MIME type pointing at a .desktop file (app launcher), it's a matter of changing that. Mine for example related to using Firefox:

    [Default Applications]
    x-scheme-handler/http=firefox.desktop
    x-scheme-handler/https=firefox.desktop

Find the .desktop file you want to launch and just update that bad boy. Most DEs have a GUI tool to manage this for you without having to resort to manual editing...

[forgotmypw17]

What does it mean that I don't have the desktop file?

[yrro]

Then you don't have a program that can handle the URL scheme, at least according to desktop-entry-spec[0], which is the source of data that xdg-utils consults.

[0] https://www.freedesktop.org/wiki/Specifications/desktop-entr...

On my (Debian) system, firefox and chromium ship their .desktop files.

[stonesweep]

nod and the .desktop file is just an INI-style file that one can hand create for anything at all, the launched app just needs to accept the URL as a parameter input as if typed on the CLI for this scheme.