Steps to reproduce the bug:

unzip the archive and open bug.html


click the 'form' button


type any text inside


click 'check for bug' button, do NOT hit 'enter' key.
a message box appears containing the text you typed


click ok, another box appears with the same text


the message box appeared twice but it's invoked differently:


the form disappears


click 'form' again, the form appears


type any text but something else than the first time


click 'check for bug' (not 'enter'), a message box with the text appears


click 'ok', another message box appears but it contains the text you typed the first time, not the text that is in the edit box


my version of firefox is 3.6.6, the test was performed in safe mode