I successfully created AT&T.app as a TenFourFoxBox application. However, when I tried to start it, I got the error message:

 You cannot open the application "AT&T" because it is not supported on this architecture.

Suspecting the ampersand, I remade the application with the name, ATT.app. But this brought a different error message:

 XML Parsing Error: not well-formed
 Location: chrome://foxbox/content/foxbox.xul
 Line Number 6, Column 32:     title="TenFourFoxBox: AT&T"

Yes, I put ampersand in the title, too. On my third attempt I changed the title to AT&T. That finally worked.

As problems go this one's minor especially with the easy work-arounds. I just posted it in case someone else runs into the same problem. It's probably not worth any more attention, so feel free to close it out.