I ran across this nifty plugin for your firefox browser when viewing Yahoo Mail. It uses AJAX and makes it possible to "preview" your emails instead of opening the entire email. Sort of how MS Outlook has the preview feature.

Preview your messages with a single click. Adds AJAX support to the Yahoo! mail. If you use Yahoo! mail just try it out.

- Preview your messages without leaving your inbox. Adds a small "plus sign" next to your email list. Click on the "plus sign" to preview the message.

- Send back messages with a single click using Instant Reply

- Download any attachment with a single click

Learn more and get it here.