Adds some integration with firefox.

This is still rather unstable, but it runs.

add-on/background.js

@@ -0,0 +1,29 @@
+var port = browser.runtime.connectNative("universal_music")
+
+/**
+ * Sends a message to the application
+ */
+function writeMessage(message)
+{
+    port.postMessage(message)
+}
+
+/**
+ * Sends a message to the application
+ */
+function onAppMessage(message)
+{
+    if ("command" in message)
+    {
+        switch (message["command"])
+        {
+        case "ping":
+            writeMessage({
+                "response": "ping"
+            });
+            break
+        }
+    }
+}
+
+port.onMessage.addListener(onAppMessage);