master - bleeding edge. exciting new features, exciting new bugs.
stable - tries to be bug free.
firefox < 4 is not supported. deal with it.
firefox: if you get a security error involving localStorage (check your error console with ctrl+shift+j), go to about:config and enable dom.storage.enabled.
For youtube embedding / linkification, check out YouLink, which works on the entire web, not just 4chon.
for exhentai sauce, check out ExSauce.