There has been added support for a small funky feature in Mozilla Mail. The news "spoiler" feature. The feature is explained at NewsReaders.com:
When reading groups like rec.arts.sf.written and alt.tv.buffy-v-slayer, people frequently don't want to have their enjoyment of works they haven't seen/read yet "spoiled" by finding out what is going to happen in advance. To help them avoid it, posters are encouraged to insert the "spoiler char" (aka form-feed, 0x0C, control-L) -- when newsreaders encounter this character they take various steps to prevent the reader from seeing the rest of the message.
Read more in bug 11080.