Change Firefox HTTP_USER_AGENT

Fire firefox
F6, hit about:config
Create new setting:
 key:
   general.useragent.override
 value:
   Mozilla/5.0 (X19; U; Linux i986; en-US; rv:2.3) Gecko/20100101 Firefox/4.0

Vietnamese Unicode Fonts

http://www.echip.com.vn/echiproot/weblh/link/kho/funidhbk.htm