firefox-location/index.js

Approximates the current location of Mozilla Firefox on your system.

var osx   = process.platform === 'darwin'
var win   = process.platform === 'win32'
var other = !osx && !win
var fs    = require('fs')

if (other) {
  try {
    module.exports = require('which').sync('firefox')
  } catch (_) {
    module.exports = null
  }

} else
if (osx) {
  var regPath = '/Applications/Firefox.app/Contents/MacOS/firefox'
  var altPath = require('userhome')(regPath.slice(1))

  module.exports = fs.existsSync(regPath)
    ? regPath
    : altPath
} else {
  var suffix = '\\Mozilla Firefox\\firefox.exe'
  module.exports = [
      process.env.LOCALAPPDATA
    , process.env.PROGRAMFILES
    , process.env['PROGRAMFILES(X86)']
  ].reduce(function (existing, prefix) {
    var exe = prefix + suffix
    return existing || fs.existsSync(exe) ? exe : null
  }, null)
}