Stuck socket.io after handshake authorization

When a client connects to socket.io on my server this is what shows in the log:

   info  - handshake authorized mEc9O3ZUWHGWDFEXOETd
   debug - client authorized
   info  - handshake authorized P8qyZTT2Da_2hbc7OETe
   debug - client authorized
   info  - handshake authorized Za3KNS-01iYjSPugOETf
   debug - client authorized
   info  - handshake authorized h2TfSTE3nRzyJkiKOETg
   debug - client authorized
   info  - handshake authorized YrLDHKQuptqNeG8KOETh
   debug - client authorized
   info  - handshake authorized cW5H6R2vSro2_RO0OETi

Nothing is happening after the handshake.

With firebug, I see that the initial socket.io request is being made and returns a 200 OK, however it does not return a response like it should.

What could be causing this? Must the port that I am using be open both inbound and outbound?