Unable to Upgrade Firefox on OS X

Today I tried to upgrade Firefox 5.0.1 on my iMac to version Firefox 6, but it failed with some 'weird' error;

The operation can't be completed because the item libsmime3.dylib" is in use.

Weird because I didn't have FireFox running at the time. Removing Firefox didn't work either, since I couldn't remove it from the Trash (same error).

Turned out that I had the Cisco AnyConnect VPN installed on my system (process name: vpnagentd). To 'unload' this process enter the following in Terminal:

sudo launchctl unload /Library/LaunchDaemons/com.cisco.anyconnect.vpnagentd.plist

Install Firefox, and enable the vpnagent again by entering the following in Terminal:

sudo launchctl load /Library/LaunchDaemons/com.cisco.anyconnect.vpnagentd.plist

And all should be well.