'The operation can't be completed because the item "libsmime3.dylib" is in use.'
Well shit, whats holding onto that lib. Turns out that it was my Cisco VPN Anywhere Agent, aka vpnagentd. So I go ahead and do a:
'sudo killall vpnagentd'
Ugh and of course it restarts automatically before I can copy the files over. So what now. Oh yeah, it runs as a daemon so I need to use my old friend launchctl to unload it. The command for this is:
sudo launchctl unload /Library/LaunchDaemons/com.cisco.anyconnect.vpnagentd.plist
w00t! Now the files copy over with no problem. Now I need to put AnyConnect back into place. This can be done with:
sudo launchctl load /Library/LaunchDaemons/com.cisco.anyconnect.vpnagentd.plist
That should do it, Firefox 4 Beta up online and working again.