I know http://www.facebook.com/?m2w and http://www.facebook.com/home.php works, but only at Facebook Inc.'s mercy. They could still make these two pages recognize useragent and throw you to the mobile page, if they see fit.

So the solution would be changing the useragent permanently. It seems that not everything could change the agent successfully by change about:config or /home/user/.mozilla/microb/prefs.js

While I'm still reseraching on it, anyone would give a hints on changing the useragent permanently would greatly welcome.