My Thai wife may have found the solution herself.
She went to a Thai language website:
http://thailinuxcafe.com/html/module...name=Downloads
and downloaded some True Type Fonts for Thai (in a compressed file, that uncompressed to be an rpm for Mandrake). This Mandrake rpm installed OK on SuSE-9.3, as near as we can tell.
She then, under FireFox, selected EDIT > PREFERENCES > GENERAL > FONTS & COLORS and then under "FONTS FOR" selected "THAI". She then had to custom choose the Thai fonts under "proportional", "serif", "sans-serif" and "monospace" selections. According to my wife, it was only by her downloading the "True Type Fonts" (from the Thai web site), that she was able to get the extra font selections needed to customise her FireFox under the "proportional", "serif", "sans-serif" and "monospace" selections. When we tried to do this on my PC's linux (where I did not download the True Type Fonts), we could not customize the Firefox.
Of course, the Thai web site with Thai fonts, being in Thai, meant I was completely useless, when it came to helping her in this.
Still, she seems reasonably happy now with the Firefox fonts, although she was complaining Firefox (for Linux) font control is more like Netscape 4.7, and its not as good as the more recent Netscape versions (for WinXP).