I have just been entering a comment, pressed CTRL-Z a few times in order to improve the wording, and suddenly my comment disappeared (or used white text color, whatsoever).
When trying to re-enter the comment (or to comment on a different question), still the text dows not appear (or in an invisible color).
The problem just disappeared after closing and restarting Firefox.
Is this a known StackExchange bug?
(And if so, does anyone mind?)