Don't have time to really research this any further, but I think I found out why I couldn't start Selenium today using my normal command line invocation. I was getting this when I tried to start it:
java.net.BindException: Address already in use
Hmmm... hadn't started it before sitting down for work.... so.... what could be the issue? How did port 4444 get bound already? A little...
PORT STATE SERVICE 4444/tcp open krb524
krb524?!? I don't remember firing that up. What is it? Well, if you do a search for "krb524 4444," you'll quickly see that "krb524" has to do with Kerberos and it seems that Kerberos is using port 4444.
I'm on a Cisco VPN. Does the Cisco VPN use Kerberos? I don't know, but it's plausible enough for me to chalk it up to that and pass a new port (something clever like -p 4445) to the Selenium JAR and whoomp - as they say - there it is.