Fast Dial

Fast Dial replaces “about:blank” page with a panel of thumbnails of your favorite sites. Click on an empty cell, assign a site URL, click OK - a thumbnail will be generated for a site. You can also add sites opened in browser or existing bookmarks by right-clicking them and choosing “Add to Fast Dial” from context menu.
https://addons.mozilla.org/en-US/firefox/addon/5721

Forecastfox™

Get international weather forecasts from AccuWeather.com, and display it in any toolbar or statusbar with this highly customizable and unobtrusive extension.
https://addons.mozilla.org/en-US/firefox/addon/398

Better Gmail

Add useful extra features and skins to Gmail, like hierarchical labels, macros, file attachment icons, and more.

Better Gmail 2 compiles the best Greasemonkey user scripts for Gmail into a single package. All scripts copyright their original authors. Click on the script homepage in the About tab for help and more information. Only compatible with the new Gmail interface.
https://addons.mozilla.org/en-US/firefox/addon/6076

GooglePreview

Inserts preview images (thumbnails) of web sites into the Google and Yahoo search results pages. The GooglePreview thumbnail system currently consists of 7 dedicated servers and generates 5 TB of traffic per month.
https://addons.mozilla.org/en-US/firefox/addon/189

FireGestures

A customizable mouse gestures extension which enables you to execute various commands and user scripts with five types of gestures.
https://addons.mozilla.org/en-US/firefox/addon/6366