fix: Look for other paths for Firefox Nightly on Windows and Mac

More recent installs of Firefox Nightly on Windows use "Firefox Nightly"
instead of "Nightly" for the application folder. Apparently OSX uses
"Firefox Nightly" instead of "FirefoxNightly" too.

index.js

@@ -52,18 +52,18 @@ var getFirefoxExe = function (firefoxDirName) {
     return null
   }
 
-  var prefix
-  var prefixes = getAllPrefixes()
-  var suffix = '\\' + firefoxDirName + '\\firefox.exe'
+  var firefoxDirNames = Array.prototype.slice.call(arguments)
 
-  for (var i = 0; i < prefixes.length; i++) {
-    prefix = prefixes[i]
-    if (fs.existsSync(prefix + suffix)) {
-      return prefix + suffix
+  for (var prefix of getAllPrefixes()) {
+    for (var dir of firefoxDirNames) {
+      var candidate = path.join(prefix, dir, 'firefox.exe')
+      if (fs.existsSync(candidate)) {
+        return candidate
+      }
     }
   }
 
-  return 'C:\\Program Files' + suffix
+  return path.join('C:\\Program Files', firefoxDirNames[0], 'firefox.exe')
 }
 
 var getFirefoxWithFallbackOnOSX = function () {
@@ -213,8 +213,8 @@ FirefoxNightlyBrowser.prototype = {
 
   DEFAULT_CMD: {
     linux: 'firefox',
-    darwin: getFirefoxWithFallbackOnOSX('FirefoxNightly'),
-    win32: getFirefoxExe('Nightly')
+    darwin: getFirefoxWithFallbackOnOSX('FirefoxNightly', 'Firefox Nightly'),
+    win32: getFirefoxExe('Nightly', 'Firefox Nightly')
   },
   ENV_CMD: 'FIREFOX_NIGHTLY_BIN'
 }