Can you reach firefly’s adminpage?
If so, you should be able to reach fireplay too.
However, ‘streaming’ the music might not work due to the proxy.
I can not reach my adminpage when I behind a proxy :-(.
However, I can hear radio streams behind this proxy when I am using winamp shoutcast radio (with this special settings like user and password for that proxy). Are there any changes to fill this settings also into the fireplay add-on?