Something very strange is going on:
You will notice at the top that Openbox is displaying the characters properly on the window decoration, so it's not lack of Chinese fonts. I checked and ttf-wqy-microhei and ttf-wqy-zenhei are both installed. It's not encoding either since browser encoding matched page encoding (UTF-8). Chinese characters are either blank or a confused jumble of symbols. What is going on here?
FWIW I had this issue before installing the latest version of Firefox but it only started to bug me recently.