Perfom a ShellExecute from Firefox Addon

Question

In my Firefox extensions I want to open certain files with the \"default viewer\" for that file type in Windows. So basically something similar to the ShellExecute(\'OPEN\

Answer 1

Files

The closest thing is nsIFile::launch. However, it is not implemented for every conceivable platform (but it is implemented at least for Windows, OSX, GTK/Gnome and compatible, KDE and Android).

You cannot use ::launch to instruct the OS (in particular Windows) to use a verb other than open, though, so there is no equivalent to e.g. ShellExecute(..., "edit", ...).

Here is a sample on how to use it:

try {
  var file = Services.dirsvc.get("Desk", Ci.nsIFile);
  file.append("screenshot.png");
  file.launch();
}
catch (ex) {
  // Failed to launch because e.g. the OS returned an error
  // or the file does not exist,
  // or this function is simply not implemented for a particular platform.
}

You can of course create an nsIFile instance from "raw" paths as well, e.g. (I'm on OSX):

var file = Cc["@mozilla.org/file/local;1"].createInstance(Ci.nsIFile);

Cc and Ci are shortcuts to Components.classes and Components.interfaces that most of the mozilla and add-ons code uses. In the Add-on SDK you can get these via the Chrome Authority.

URIs

Edit I totally forgot that ShellExcute will also handle URLs. And you did ask only about "file type[s]", BTW.

Anyway, to open a random URI, you can use the nsIExternalProtocolService.

Option 1 - Launch with the default handler (not necessarily OS handler)

To launch with a default handler, which could also be a web protocol handler or similar, you can use the following code. Note that this might show a "Select application" dialog, when the user didn't choose a default for a protocol yet.

var uri = Services.io.newURI("https://google.com/", null, null);
var eps = Cc["@mozilla.org/uriloader/external-protocol-service;1"]
          .getService(Ci.nsIExternalProtocolService);
// You're allowed to omit the second parameter if you don't have a window.
eps.loadURI(uri, window);

Option 2 - Launch with the OS default handler, if any

If Firefox can find an OS default handler for a particular protocol, then the code will launch that default handler without user interaction, meaning you should be extra careful not to launch arbitrary URIs that might do harm (e.g. vbscript:...)!

var uri = Services.io.newURI("https://google.com/", null, null);
var eps = Cc["@mozilla.org/uriloader/external-protocol-service;1"]
          .getService(Ci.nsIExternalProtocolService);
var found = {};
var handler = eps.getProtocolHandlerInfoFromOS(uri.scheme, found);
if (found.value && handler && handler.hasDefaultHandler) {
  handler.preferredAction = Ci.nsIHandlerInfo.useSystemDefault;
  // You're allowed to omit the second parameter if you don't have a window.
  handler.launchWithURI(uri, window);
}