As those pages refered, you should insert a base Thai character (U+0E01—U+0E2F) firstly, than you add so many Thai marks on it. Then you will see these marks will placed continuously on a Thai character. To my eyes, the following texts copied from those web pages can make the effect (thin effect can’t appearing in FreeSerif):

ฒุุุุุูููููิิิิิ่่่่่ีีีีี้้้้้ึึึึึ๊๊๊๊๊ืืืืื๋๋๋๋๋ััััั๎๎๎๎๎์์์์, ปึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึ, ปึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึึ, อุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุุ, ดัััััััััััััััััััััััััััััััััััััััััััั, ฏ๎๎๎๎๎๎๎๎๎, ด้้้้้็็็็็้้้้้็็็็็้้้้้็็็้็็็, ฏ๎็็็็็็,

Hi Steve,

Thai script has become internet meme in Chinese netizens. They put so many vowel marks to a base letter to make them so height that can be “insert” into other comment. As they mentioned, these phenomenons can works with Windows 7, some web browsers as Firefox also displaying proper. I copied some of them, found they are failed to rendering in FreeSerif. I don’t know which table can impelement these phenomenons? You can found these sequences in following pages:

http://tieba.baidu.com/p/3206721382
http://tieba.baidu.com/p/1939061891