Add firefox launcher back in

Karma seems to have dropped it as a "default"

Author: dfreedm

package.json

@@ -11,6 +11,7 @@
     "grunt-karma": "*",
     "karma-mocha": "*",
     "karma-ie-launcher": "*",
+    "karma-firefox-launcher": "*",
     "karma-safari-launcher": "*",
     "karma-script-launcher": "*",
     "karma-crbot-reporter": "*",