Custom Buttons Requires Restart
Gives a possibility to create custom toolbarbuttons...
Save better history for fragment URLs.
MonkeyFix Requires Restart
Fixes up numerous SeaMonkey browser interface issues (eg. adding support for popup ALT attributes), as well as adding some handy features for developers and power users (eg. configure source viewer, work online/offline).
TaQuilla Requires Restart
Automatic tagging using Bayesian statistics
CuteMenus - Crystal SVG Requires Restart
Note from Mozilla: This add-on has been discontinued. Try Menu Icons Plus instead.
Adds icons to all menus along with some other features...
FireTray Requires Restart
A system tray extension for Linux and Windows, allowing to set up custom icon, hiding to tray instead of closing, display the number of unread messages in mailing applications, and other features ...
Block advertisement and access to adult sites
Duplicate This Tab Requires Restart
This add-on provides the much needed feature update of Tab Duplication to Mozilla Browsers. Features Supported include Duplication of Browser Tabs, Detaching Tabs and Merging All Windows.
Blue Essence Seamonkey Theme Requires Restart
Dark navigator theme based on a default Classical theme and now works on Linux :)
Forecastfox Weather Requires Restart
Get international weather forecasts from AccuWeather.com and display them in any toolbar or statusbar with this highly customizable and unobtrusive extension.
Show all the menus in a single menu button that can be placed anywhere. Also contains replacement buttons for the default menus.
Changes the mask character used in password fields.
CloseTab Requires Restart
Lightweight add-on which adds to right-click menu 3 items allowing to close current tab, open a new one and reopen closed one. Right-click anywhere on site instead of using keyboard or finding buttons.
Adds a few buttons to help with page navigation, including Page Top, Page Bottom, Page Down and Page Up.
printplus Requires Restart
PDF export support by Gecko.
Want to change from one language to another? Zing! and the locale is switched.
NiceReader Requires Restart
NiceReader is designed for web reading. You can customize font, color, size, background, specify the elements to read, filiter ad elements, filiter ad strings, automaticaly turn page.
RC Print Requires Restart
Adds a "Print" option to the Right-Click context menu.
MonkeyMenu Requires Restart
MonkeyMenu brings some of the features of the MenuX Firefox extension to the Seamonkey browser. You can add about 29 buttons to the Seamonkey user interface, collapse any toolbar, add/remove search engines, have your font zoom size reloaded, and...
Makes every page to have light text on dark background (exact colors are customizable)
Firefox version is here: https://addons.mozilla.org/firefox/addon/dark-background-light-text/