Here are the list of packages I installed along with firefox to get X11 programs running within a  solaris 11 zone:

pkg install SUNWarc SUNWbtool SUNWhea SUNWlibms xorg-iso8859-1 SUNWmfrun SUNWxorg-client-programs SUNWxorg-clientlibs SUNWxwfsw pkg://solaris/SUNWxwplt truetype/fonts-core

Thanks to this post for the starting point -- I've added ttf fonts to the original procedure

Update:  seems xorg-iso8859-1 causes problems, so use:
pkg install SUNWarc SUNWbtool SUNWhea SUNWlibms SUNWmfrun SUNWxorg-client-programs SUNWxorg-clientlibs SUNWxwfsw pkg://solaris/SUNWxwplt truetype/fonts-core