I can launch Thunderbird or firefox from any computer, even at work with a firewall. However only one app at a time, when one is open opening the other will give an error message that it is already running. I have tried this on Vista and win2K with the same results.
for both applications. Delete both applications. Reinstall both applications. Restore you profiles.
Not sure what the exact issue is, but it sounds like you have some launcher issues with one or both apps. A reinstall should do it.
Life is about the journey not the destination!
The Kazoo Spartan