Why can't I right-click "Paste" or "Cut" in Gmail and Yahoo! mail?

I have FF 1.5.0.4 and Windows XP Home. When I go to compose an email in
Gmail or Yahoo, the "cut" and "paste" commands don't appear when I hit
right-click in the text area.

If I change the formatting to plain text, it works fine, but I'd rather use
the rich text format. This isn't a problem in IE.

Thanks.

Joe Jorgenson