I know XPCOM isn’t all that popular anymore.
However, I’d still like to hack on some Firefox internals using the XPCOM C++ ABI.

Following this (quite outdated) sample and the following moz.build I end up with quite a few errors when running ./mach build from the gecko-dev root directory. Errors I’m unable to fix on my own.

moz.build

XPIDL_MODULE = 'sample'

XPIDL_SOURCES += [
  'nsISample.idl',
]

SOURCES += [
  'nsSample.cpp',
]

FINAL_LIBRARY = 'xul'

Is there any more recent documentation available?