following on from what guy said
a browser doesn't listen on ports in use(I don't think any client or server can, by definition, otherwise the OS wouldn't know what process, specifically what particular connection- to send the packet to). the browser finds a port not in use.
http://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers
not under 1024 and in fact not under 49152! so very high numbered ports. that ephemeral port range 49152–65535
if you knew basic use of netstat it'd make you more familiar with things.
Try from a cmd prompt, netstat -aon or netstat -n and look at the output.
here's an example from netstat -n
you see two columns of IPs, one local, one remote (so it won't show you whether a connection is incoming or outgoing).. an ip that relates to your computer is shown on the left hand side. look on the right hand side see the lines where the right hand side have :80 only one row in this case but typically many, now see the port on the left hand side chosen by the browser e.g. 50714
if you do netstat -on or -aon then, the -o gets you a column for process id, and you can see in task manager which process is which.