The short version:
How do I start up Karma and have it open the debug.html file automatically in the same browser as the Karma start page?
You can use a customLauncher browser definition:
customLauncher
customLaunchers: { ChromeDebugging: { base: 'Chrome', flags: [ '--remote-debugging-port=9333', '--auto-open-devtools-for-tabs', 'http://localhost:9876/debug.html' ] } }
And use this browser in your karma config.