Firefox Extension using Native Messaging to get a website's IP address and check it against a scope file.

Web extensions (add-ons) are written in JavaScript which can't resolve DNS. Most extensions get around this by the following: When a user visits a site, the extension sends the website's URL to an API server via an HTTP request. The API server then resolves the recieved URL's IP address and replies with it.

This results in the API server's ability to track the user. Every website the user visits is sent to the API server. If the user visits an internal site, the internal naming convention will be exposed to the API server. Additionally, the external server will lack access to the internal DNS server and fail to resolve the domain properly.

In contrast, inscope uses Firefox's Native Messaging API to send the domain names to a Python script running locally on the user's system. That script just calls socket.gethostbyname. The web browser has already resolved the domain name, so the system should still have it in the cache. This results in an increase in speed and privacy.

The only downside of Native Messaging is a slightly more complicated installation process.

Just installing inscope lets you quickly get the IP address of a website on mouseover of the inscope icon.

If you create a /tmp/ff_scope file containing a new line separated list of IP addresses. When the Python script resolves an IP, it will check if that IP is in the provided list. If so it will make the inscope icon turn green . Otherwise it will be red . If the /tmp/ff_scope file is updated, clicking the inscope icon will tell it to re-parse the file.

This is still very new. Pull requests or notifications of issues are welcome.

There are two parts to the installation. The web extension must be added to Firefox. Then Firefox must be notified where the native application is located.

Add the .xpi file to Firefox, which is explained here.

1. Move src/app/inscope.py to a desired location. For security the directory should not be world writable. Ensure the file permissions are set to executable.

2. Move the manifest file from src/app/inscope.json to a directory in which Firefox will look. See Firefox documentation

3. Replace the path variable in the manifest file (src/app/inscope.json) with the full path to the Python script (inscope.py)

4. Reload the extension in Firefox and check the console for errors.

The install.sh script was written to do the Native Application install, on Linux, the way I like it. It should be reviewed before running; it may not be ideal for your use case.