Yes, the nefarious Netscape strikes again. You cannot add an email address
to a new mesage using the Address book. (Typing it in works)

The answer is to remove any lines containing the word 'locale' from 
~/.netscape/libprefs.js or preferences.js 

Can the Netscape rpm's be altered to correct this? Probably not if the *.js
files are generated on the first use of Netscape.  Unless you have real
source to work with.