Automated tests: DevTools mochitests

To run the whole suite of browser mochitests for DevTools (sit back and relax):

./mach mochitest --subsuite devtools --tag devtools

To run a specific tool's suite of browser mochitests:

./mach mochitest devtools/client/<tool>

For example, run all of the debugger browser mochitests:

./mach mochitest devtools/client/debugger

To run a specific DevTools mochitest:

./mach mochitest devtools/client/path/to/the/test_you_want_to_run.js

Note that the mochitests must have focus while running.