Is there any way to start an application by using an (already registered) URI scheme from my extension's code?
I want to monitor something through background.js and start an app by URI scheme automatically
You can do so by appending an iframe
to your background page.
Again with the Steam example:
var frame = document.createElement("iframe");
frame.src = "steam://open/main";
// Needs to be inserted into document to trigger load
document.body.appendChild(frame);
document.body.removeChild(frame);