AJAXify Yahoo! Mail - Today's Browser Tip
Once again, Greasemonkey does not fail to amaze. Vivek Jishtu has written AJAX for Yahoo! Mail, a Greasemonkey user script (or stand-alone Firefox extension, take your pick) which, in case you hadn't guessed, adds fancy AJAX features to Yahoo! Mail, including message previews and "instant reply." This, at least, will do a bit to fill the Gmail gap while Yahoo! Mail users wait for the next version of Yahoo! Mail and its Oddpost-inherited features.