This is a very simple example of how to use native messaging to exchange messages between a WebExtension and a native application.

The WebExtension, which can be found under "add-on", connects to the native application and listens to messages from it. It then sends a message to the native application when the user clicks on the WebExtension's browser action. The message payload is just "ping".

The native application, which can be found under "app", listens for messages from the WebExtension. When it receives a message, the native application sends a response message whose payload is just "pong". The native application is written in Python.

Setup

To get this working, there's a little setup to do.

Mac OS/Linux setup

1. Check that the file permissions for "ping_pong.py" include the execute permission.
2. Edit the "path" property of "ping_pong.json" to point to the location of "ping_pong.py" on your computer.
3. copy "ping_pong.json" to the correct location on your computer. See App manifest location to find the correct location for your OS.

Windows setup

1. Check you have Python installed, and that your system's PATH environment variable includes the path to Python. See Using Python on Windows. You'll need to restart the web browser after making this change, or the browser won't pick up the new environment variable.
2. Edit the "path" property of "ping_pong.json" to point to the location of "ping_pong_win.bat" on your computer. Note that you'll need to escape the Windows directory separator, like this: "path": "C:\\Users\\MDN\\native-messaging\\app\\ping_pong_win.bat".
3. Edit "ping_pong_win.bat" to refer to the location of "ping_pong.py" on your computer.
4. Add a registry key containing the path to "ping_pong.json" on your computer. See App manifest location to find details of the registry key to add.

To assist in troubleshooting on Windows, there is a script called check_config_win.py. Running this from the command line should give you an idea of any problems.

Testing the example

First, install the add-on. Visit about:debugging#/runtime/this-firefox or, from about:debugging click "This Firefox" (or "This Nightly" in the Nightly version of Firefox), click "Load Temporary Add-on", and open the add-on's "manifest.json".

Now, open the extension's console using the "Inspect" button - this is where you'll see communication between the browser and native app.

You should see a new browser action icon in the toolbar. Click it. You should see output like this in the console:

Sending: ping
Received: pong3

If you're running Python 2.x, you'll see "pong2" as the response instead.

If you don't see this output, see the Troubleshooting guide for ideas.