Socket.io returns to xhr in Firefox

Question

My application uses Node.js and Socket.io. It works fine, but when I disconnect from the Internet, Socket.io returns to xhr, but only on Firefox, On chrome works fine.

These are my debugging messages:

info - socket.io started Express server listening on port 3000 development GET /connexion 200 38ms - 882 POST /connexion 302 5ms - 64 GET /jeu 200 8ms - 583 debug - client authorized info - handshake authorized UTHMxCJEKx-DC3sSf57M debug - setting request GET /socket.io/1/xhr-polling/UTHMxCJEKx-DC3sSf57M?t=1365791206086 debug - setting poll timeout debug - client authorized for debug - clearing poll timeout debug - xhr-polling writing 1:: debug - set close timeout for client UTHMxCJEKx-DC3sSf57M debug - xhr-polling received data packet 1::/jeu/Jeu1 s:B2ZSTca4rYyle+ooJCY5/Z+d.xuW1XrVrU+IG0UpLvs5q88hm6Nr83SOwr7fpOjfPhbM B2ZSTca4rYyle+ooJCY5/Z+d debug - client authorized for /jeu/Jeu1 debug - setting request GET /socket.io/1/xhr-polling/UTHMxCJEKx-DC3sSf57M?t=1365791206116 debug - setting poll timeout debug - clearing poll timeout debug - xhr-polling writing 1::/jeu/Jeu1 debug - set close timeout for client UTHMxCJEKx-DC3sSf57M debug - discarding transport debug - cleared close timeout for client UTHMxCJEKx-DC3sSf57M newPlayer: hamou92 debug - broadcasting packet debug - setting request GET /socket.io/1/xhr-polling/UTHMxCJEKx-DC3sSf57M?t=1365791206203 debug - setting poll timeout debug - discarding transport debug - cleared close timeout for client UTHMxCJEKx-DC3sSf57M 

Here is what Firebug shows me:

 Firefox ne peut établir de connexion avec le serveur à l'adresse ws://localhost:3000/socket.io/1/websocket/_uQklvPYeYn-_BNg-WDa. this.websocket = new Socket(this.prepareUrl() + query); socket.io.js (ligne 2371)