You can now open Browser Toolboxes on more than one instance of Firefox

Brian Grinstead bgrinstead at
Fri Aug 25 17:37:15 UTC 2017

It used to be that if you opened the Browser Toolbox on more than one instance of Firefox, then all the Browser Toolboxes would end up connecting to the first instance. I know a lot of people have run into this problem, myself included. For instance:

  ./mach run --profile /tmp/1 --jsdebugger
  ./mach run --profile /tmp/2 --jsdebugger

Here both Browser Toolboxes would end up debugging the first instance of the browser. This is because the debugger server used a static port (6080) so when the second instance tried to start the debugger server it would fail, but the Browser Toolbox frontend didn't care and just connected to 6080 (the first instance).

I had an idea to make this better by letting you specify an explicit port for the second instance, but jryans had a much better idea, which was to randomly pick a port when starting the debugger server and send it along to the Browser Toolbox ( So it should be working automatically now - you should see dump output like: `Debugger Server for Browser Toolbox listening on port: 63148` after starting it.

Big thanks to Ryan, and happy debugging!

More information about the firefox-dev mailing list