You can see available commands with:
./mach -h ./mach <sub-command> -h
Only arguments that need more explanation will be documented here.
Use --pref to enable experimental features like experimental DOM API, JavaScript API and CSS properties.
e.g. To enable flex and flex-direction css properties:
./mach run -d -- --pref layout.flex.enabled --pref layout.flex-direction.enabled ...
You can find all the available preferences at resources/prefs.json.
Use --devtools 6000 to start the devtools server on port 6000.
e.g.
./mach run -d --devtools 6000 https://servo.org
To connect to the server, follow this guide.