In Yahoo mail, how do I cut and paste an image directly into my email?

I am using Firefox 3.6.12 and XP SP3. I don't want to add the image as an attachment. Rather, I want to cut and paste it into the text portion of the email (like you can do in Word, Powerpoint, etc.) I tried following the directions given by Yahoo in the mail help section. I AM in rich text mode (the words "plain text" appear just to the right of the subject box). I select an image, hit CTRL-C. I go to the message I'm composing in Yahoo. When I hit CTRL-V, nothing happens. If I subsequently go to Word and hit CTRL-V, the image pastes in as expected. What's wrong with Yahoo mail?