Firefox Developer Tools protocol adapters
JavaScript HTML Makefile
Latest commit ec7493e Jan 27, 2017 @jryans jryans Release 0.3.7, bump to 0.3.8


Valence is a Firefox add-on that is installed by default with Firefox Developer Edition. It is a remote debugging protocol adapter that allows you to debug Chrome and Safari (desktop and mobile) from Firefox, using WebIDE.

Documentation on how to use WebIDE and Valence is available on the Mozilla Developer Network.

How to Interact With The Thing

There are three ways to interact with this tool right now: WebIDE, some Developer Toolbar commands, or a toolbar button.

WebIDE is the main tool for debugging remote devices and this add-on provides additional runtime options in the Custom section for Chrome and iOS. You can learn more about WebIDE in the Mozilla Developer Network.

If you prefer interacting with a command-line tool, use the commands chrome, android and ios from the Developer Toolbar. These should automatically launch a browser for you and connect appropriately - assuming you've met the installation requirements below.

For a quick setup when working on the add-on itself, it will add a (weirdly ambiguous) new icon to your browser, once you set the pref to true. You can toggle its value from about:config, or by adding it in a JSON file with preference overrides that you provide to jpm via the --prefs option (check out jpm --help for the right syntax). When you click it, it will attempt to connect the Firefox DevTools to whatever is on port 9222. For example, if you start an instance of Chrome Canary on port 9222 (use flag --remote-debugging-port=9222), it will try and connect to that.

Installation for All Y'all

Before you can build and run the extension, here are a few things you'll need to do:

  1. git clone

  2. Make sure you have an updated copy of Firefox Nightly installed. If you need to install Nightly, you can get it here.

  3. Make sure you have node (and subsequently npm) installed. Instructions for that are here.

  4. Install jpm with npm install -g jpm. jpm is a node utility for developing browser add-ons.

Then from your extension folder you can use jpm run -v, with the-b option to use your recent Firefox Nightly, to run a new Firefox process with the extension installed.

Now that you've done that, you can follow the instructions below for each applicable debug target/browser.

For more detailed building instructions and instructions for building the ios-webkit-debug-proxy binaries, see building.html.

Debugging Chrome on Desktop

Clicking the button on the Firefox toolbar will connect to the debug target on port 9222. To debug Chrome on Desktop, the process must have remote debugging enabled and set to this port.

The important flag is --remote-debugging-port=9222. There is a page with information on how to run the Chrome process with these flags.

There are some other flags that can be helpful if you'd like to run this alongside another Chrome profile. By running with --no-first-run, --no-default-browser-check, and --user-data-dir you can run this process alongside another Chrome profile.

For example, on OSX, you could run the following command to start a debuggable copy of Chrome:

> /Applications/Google\\ Chrome --remote-debugging-port=9222 --no-first-run --no-default-browser-check --user-data-dir=$(mktemp -d -t 'chrome-remote_data_dir')

If you click on the toolbar button and nothing happens, you most likely don't have anything running on port 9222. Check the Browser Console to see what has gone wrong.

Debugging Chrome on Android

In addition to the installation instructions, follow these instructions to turn on remote debugging and set up adb.

Debugging Safari, Firefox, and other WebViews on iOS

In addition to the installation instructions, you will need to enable developer support on your device. Follow the instructions on this page (in the "To enable Web Inspector on iOS" section) to get started. Note: you can also use the iOS simulator if you have Xcode installed.

Debugging Safari, Firefox, and other WebViews on iOS is possible through the use of the following open source libraries that come bundled with this extension:

  1. ios_webkit_debug_proxy version 1.4 on both OS X and Linux
  2. libimobiledevice version 1.1.5 on OS X, 1.2.0pre on Linux
  3. libplist version 1.10 on OS X, 1.12pre on Linux
  4. libusbmuxd version 1.0.8 on OS X, 1.0.0pre on Linux

On Windows we are using the ios-webkit-debug-proxy port at commit 20679aaa990b82e7fb43e434e271cce17e327f90. An additional runtime requirement on Windows is to have iTunes installed, or at least the Apple Mobile Device Support and Apple Application Support applications that come with it.

Why did you start this project?

We realized that debugging individual browsers in their respective vendor silos is painful, frustrating, and at times downright demoralizing. We wanted to make better tools so that web developers are relieved of this anguish (as much as possible). You should test this thing as it becomes more stable, and let us know how we can make the cross-platform debugging experience better.


Note that this project should be treated as ALPHA software - implementation is far from finished.

The UI for interacting with this project will change soon - the commands will likely stick around but the ambiguous button in your browser will probably not. Eventually there will even be nicer buttons than any of this. Dare to dream.

If you notice that the install or usage instructions should be different, please help us by sending a PR for this README. This project is changing fast and so information here may be out of date.