$ MOZCONFIG=./mozconfig-firefox-opt ./mach eslint 0:00.12 Running /usr/local/bin/eslint 0:00.12 /usr/local/bin/eslint --plugin html --ext [.js,.jsm,.jsx,.xml,.html] . /testing/eslint-plugin-mozilla/lib/processors/xbl-bindings.js:12 const NS_XBL = "http://www.mozilla.org/xbl"; ^^^^^ SyntaxError: Use of const in strict mode. at Module._compile (module.js:439:25) at Object.Module._extensions..js (module.js:474:10) at Module.load (module.js:356:32) at Function.Module._load (module.js:312:12) at Module.require (module.js:364:17) at require (module.js:380:17) at Object.<anonymous> (/mnt/desktop/gecko/testing/eslint-plugin-mozilla/lib/index.js:17:13) at Module._compile (module.js:456:26) at Object.Module._extensions..js (module.js:474:10) at Module.load (module.js:356:32) 0:38.61 Finished eslint. Errors encountered.

You need to have at least Node 4.2 installed, you have an older version. We're going to be adding some sanity checks for things like this in bug 1239139.