[LaunchPad] Detecting running firefox depends on OS and connectionPort

[th7nder]

When you launch browser manually, not via "Launch Firefox" button - launchpad does not detect it.
It is because of a way of searching running processes. It strongly depends on arguments passed to the firefox-bin. So when you switch to a different connection port, OS or tcp/websocket it doesn't work.

https://github.com/firefox-devtools/devtools-core/blob/master/packages/devtools-launchpad/src/server/utils/firefox.js#L20

As @jasonLaster suggested on slack, probably we should change it to -start-debugger-server making it compatible.