http://en.wikipedia.org/wiki/Text-to-voice. TTS gives Firefox the power of speech. Select text, click the button on the bottom right of Firefox window and this add-on speaks the selected text for you. Isn't it brilliant? Audio is downloadable.
Google Search by Image:
Use rightclick on an image to quickly find out the source of an image, how it is used, or find higher resolution versions via Google Reverse Image search.
(Google Image Search is similar to Tineye Reverse image search).
Instant access to the best websites related to the site you are browsing!
GProxy lets you set and clear GPass local proxy in Firefox and Thunderbird, and do more.
Adds the number of unread messages and chat notifications in Gmail to the favicon. This addon is now compatible with Firefox 4.0, as appears to work with Gmail at the time of this update. (May 11th, 2011.)