referer-mod

Referer Modifier is a Web Extension for Firefox to modify the Referer header in HTTP requests, and the Javascript document.referrer property to match. For each target domain, one of five actions can be configured:

• Keep: Do not modify the Referer
• Prune: Send only the origin part of the Referer (scheme, host, and port)
• Target: Send the origin of the target URL (scheme, host, and port) as Referer
• Remove: Send no Referer at all
• Replace: Replace the Referer with a configured value

You can configure default actions for requests originating from the same domain, and any other request not matching a domain rule. The "replace" and "target" actions will create a Referer header if necessary, the others only modify or remove existing ones. The configuration can be exported as and imported from JSON files.

Installation

Users should install the add-on from the addons.mozilla.org page.

If you're working on the code you can load your work in progress as a temporary add-on using the Firefox about:debugging page.

Developer information

The following files implement the core functionality:

• engine.js defines the functions used to determine if and how the referrer values should be modified. This code is shared by background and content scripts.

• background.js does initialization and contains the handler function modifyReferer(e) to modify headers. The handler function is called from an asynchronous webRequest.onBeforeSendHeaders event listener. background.js also uses event listeners to update the internal configuration if it is changed via the settings page. A dynamic content script containing the configuration is added to sites, for use by content.js.

• options.html is the settings page. The value attributes of the option elements inside the select elements with class="action" must match the cases handled in the modifyReferer(e) function.

• options.js handles loading and saving the settings from the settings page.

• content.js is a content script that modifies the document.referrer property to match the HTTP Referer header.

Settings are saved in the browser.storage.sync storage area, so if the user is using Firefox sync their settings will be synchronized automatically, otherwise the storage is local.

There is limited localization data in the _locales/ directory. The Makefile serves to build a ZIP archive for upload to AMO.

The repository contains a configuration file for ESLint. ESLint runs in CI (see the "Referer Mod / lint" job), please pay attention to its results when working on a pull request.

Testing

The testserver/ directory of this repository contains a test environment based on Go and Docker that you can use locally. You can use it manually (see the README), or run test.py for automated tests. The automated tests require the Selenium Python client and Geckodriver.