Adds some integration with firefox.

This is still rather unstable, but it runs.

add-on/intermediary_manifest.json

@@ -0,0 +1,7 @@
+{
+  "name": "universal_music",
+  "description": "A link between the Universal Music Player and the web browser.",
+  "path": "${LINK_PATH}",
+  "type": "stdio",
+  "allowed_extensions": ["universal_music@regis.edu"]
+}