feat: Added --firefox-debugger-socket option

[yureitzk]

This allows connecting to Firefox on Android devices without access to /proc/net/unix, bypassing automatic socket discovery.

[Rob--W]

Could you elaborate when this would be needed, and how we can test it?

The current logic matches Firefox's logic that is used at about:debugging on desktop. There, we also parse /proc/net/unix without fallback, see this Firefox source code: https://searchfox.org/firefox-main/rev/28398d11d39984cc5db08020671e7dd0d1408ec0/devtools/client/shared/remote-debugging/adb/adb-device.js#29-40

[yureitzk]

Yes. The problem is that new version of Android don't have an access to /proc/net/unix on non-root devices, and the current code fails to extract Firefox's socket. This option allows user to skip the file check and manually specify the socket.

The socket usually looks like this @org.mozilla.fenix/firefox-debugger-socket . It's pretty much the same string you parse from /proc/net/unix. To test the connection in the code I make a temporary FirefoxRDPClient and make a test connection on it. Not sure if that's the best to test the connection though, but without it, the program will fail with a cryptic error for an end-user

[Rob--W]

You linked to a restriction for apps in Android 10. I have tested various Android versions on different Pixel devices without issues.

Which phone are you using?
What OS is it running?
What is the output of:
adb shell cat /proc/net/unix
adb shell ls -la /proc/net/unix

[yureitzk]

I think I figured it out. Some of my phones (running Android 10+) have access to /proc/net/unix, and dome don't. The ones that can't access it are running custom ROMs that set the file's permissions to 440, so you can't really open the file via adb, you need a root shell

[Rob--W]

If you have a root shell you can fix up your permissions yourself. For example, here is a (random) other project where a similar access issue was encountered, and a user shared explicit steps to fix it up temporarily: mpotthoff/vscode-android-webview-debug#4 (comment)

[yureitzk]

For sure, you can change the permissions, but doing this just to test a web extension is not really handy, especially if you rely on 440 mask and you need to change it each time you want to test a web extension on your phone

spam

[Rob--W]

/proc/net/unix 440 is not a standard configuration, and prevents web-ext from discovering debugging targets.

Allowing users to specify a custom debugging socket is a footgun, because it would result in an attempt to connect to the wrong app.

We'd be willing to consider a safe patch that just falls back to trying to detect the presence of the abstract socket by its well-known name if /proc/net/unix is unreachable. When web-ext runs a Firefox app, it already knows which appid it wants to launch, so you could use that to construct the socket path.

To enable the use of about:debugging in Firefox, a similar patch would be needed for Firefox though. Otherwise you can start an extension with web-ext, but not be able to debug it via about:debugging.