packages like galeon and yelp need a geck engine installed which is porvided by various packages (e.g. mozilla, mozilla-firefox, seamonkey). Instead of using a use flag, I'd suggest to add a virtual package for the gecko engine.
Created attachment 98154 [details] An ebuild for a virtual gecko package
Except that it doesn't work for lots of packages still (and www-client/mozilla plain shouldn't be there, it needs to be p.masked and removed). Please, read the other bug. *** This bug has been marked as a duplicate of 137665 ***