Title: Using Firefox remote debugging feature

	Title: Using Firefox remote debugging feature
	Author: Solène
	Date: 06 August 2024
	Tags: firefox network
	Description: In this blog post, you will learn how to use Firefox
	remote debugging feature

	# Introduction

	Firefox has an interesting features for developers, its ability to
	connect a Firefox developers tools to a remote Firefox instance. This
	can really interesting in the case of a remote kiosk display for
	instance.
	The remote debugging does not provide a display of the remote, but it
	gives you access to the developer tools for tabs opened on the remote.

	# Setup

	The remote firefox you want to connect to must be started using the
	command line parameter `--start-debugger-server`. This will make it
	listen on the TCP port 6000 on 127.0.0.1. Be careful, there is another
	option named `remote-debugging-port` which is not what you want here,
	but the names can be confusing (trust me, I wasted too much time
	because of this).

	Before starting Firefox, a few knobs must be modified in its
	configuration. Either search for the options in `about:config` or
	create a `user.js` file in the Firefox profile directory with the
	following content:

	```
	user_pref("devtools.chrome.enabled", true);
	user_pref("devtools.debugger.remote-enabled", true);
	user_pref("devtools.debugger.prompt-connection", false);
	```

	This enables the remote management and removes a prompt upon each
	connection, while this is a good safety measure, it is not practical
	for remote debugging.

	When you start Firefox, the URL input bar should have a red background.

	# Remote connection

	Now, you need to make a SSH tunnel to that remote host where Firefox is
	running in order to connect to the port. Depending on your use case, a
	local NAT could be done to expose the port to a network interface or
	VPN interface, but pay attention to security as this would allow anyone
	on the network to control the Firefox instance.

	The SSH tunnel is quite standard: `ssh -L 6001:127.0.0.1:6000`, the
	remote port 6000 is exposed locally as 6001, this is important because
	your own Firefox may be using the port 6000 for some reasons.

	In your own local Firefox instance, visit the page `about:debugging`,
	add the remote instance `localhost:6001` and then click on Connect on
	its name on the left panel. Congratulations, you have access to the
	remote instance for debugging or profiling websites.

	Input the remote address localhost:6001 and click on Add

	Click on connect on the left

	Enjoy your remote debugging session


	# Conclusion

	While it can be tricky to debug a system you can directly see,
	especially if it is a kiosk in production that you can see / use in
	case of a problem.