I've seen this before -- and I'm seeing it right now. I don't know whether there is a solution for end users. There might be a solution for webmasters (selecting a different font).

Thanks a reply. That's a good hint.

Problem has solved when i unchecked an option:

Tools - Options - Content - Fonts&Colours - Advanced - "Allow pages to choose their own fonts, instead of my selections above"

Then, i changed fonts manually for each languages (Western, Thailand and other)

Is it a problem of website? (But symptom is not occur on my Portege R500 with windows XP in spite of same version of firefox and same font...)