On the FF3 browser, try this; [if you haven't already :) ]
Click tools then options
Click Content tab.
Untick block pop ups - tick load images automatically-
tick enable javascript -tick enable java.
Then ctrl and R to refresh the browser and try inserting a game again.
I tried clearing all the cookies and it didn't help, but when I try to put a game in to the posting box via "Insert Game or Position" it just hangs, and if I click the Chess Wizard tab it'll pop up with the first screen, where you select what type of position/game you want to insert, but when I click continue, nothing happens. Not sure if this is common or just a problem for me.