Read this: There appears to be a limit

But is there really?

Yes and no is the answer… Yes there is if you use rtmpt or rtmpte via http. But if you’re using a non-tunneling connection apparently not – I have tested a real AS3/FMS3 TextChat application that uses 20+ simultaneous connections to seperate chat room instance and someone else claims to have proved 100!

This is possible because RTMP, RTMPE etc uses TCP which is a point to point protocol which doesn’t use the browser.

Brian Lesser Explains:

When Flash connects via HTTP/HTTPS I believe it works with the browser to establish the connection. If you are using HTTP calls or Flash Remoting calls, I think you will see connection limits with IE.

When Flash connects via RTMP or RTMPE to Flash Media server, the Flash player opens a TCP socket directly and does not use the browser at all. It is only when RTMP must be tunneled via HTTP that I think Flash uses the browser and would suffer any browser imposed connection limits.

So while you should not hit a connection limit imposed by the browser all the time I think you may do so when you must fall back to tunneling RTMP. Really this is a question for an Adobe engineer though…

Also watch out for this bug RTMPT Bug?