Menu Editor II Requires Restart

Hides or moves menus and menu items. (Deprecated version, see below.)

Y U no validate Requires Restart

In the "Add Security Exception" dialog makes "Permanently store this exception" checkbox unchecked by default.

Previously known as XULernia. New name seems to be less misleading.

Tooltip Plus Requires Restart

Show tooltips for links and images with URLs, icons, alt text, and long titles.

Link Status Requires Restart

Shows an icon on the status bar when the mouse cursor is over a link to a page you bookmarked or visited before. In Firefox 3.5 and later, the extension also offers an option to disable the visited link styling to reduce the risk to privacy.

Random Theme Switcher Requires Restart

This extension switches your themes at random.

Personas Windows Classic Statusbar Requires Restart

“Personas” add-on installed, but bottom status bar still gray? This add-on modifies style so Personas footer can show. For desktop's gray “Windows Classic” theme (only Windows 2000 theme) with “Default” app theme. Requires Personas add-on ≤1.5.*.

System Monitor Requires Restart

Provides CPU usage and memory usage graphs on the toolbar.

Autohide Tabbar Requires Restart

This extension auto-hides the tab bar.

Splash! (Compatibility Update) Requires Restart

Adds a splash screen. Supported in Firefox, Flock, Thunderbird, Sunbird, eMusic Remote, Songbird and Sunbird.

xultray for gecko 1.9.2 Requires Restart

Show xul application (gecko 1.9.2 based) in system tray. supports Firefox 3.6 / 3.7 , Thunderbird 3.1

xultray for gecko 1.9.1 Requires Restart

Show xul application (gecko 1.9.1 based) in system tray. supports Firefox 3.5, Thunderbird 3.0.

ZenbuShiitake Requires Restart

IMEStatus Requires Restart

Show IME status by input/textarea/textbox background color.

Personasizer

Personasizer allows you to expose more of your persona's header image. Useful for personas that have text or an important part of their content cut off by the browser's navigation elements.

WebMyStyles

Style the web your way- provides a GUI that allow web users to change the look-and-feel of arbitrary web pages to something more pleasant and accessible.

Password Mask Changer

Changes the mask character used in password fields.

No Close Other Tabs Requires Restart

Removes "Close other tabs" context menu item.

Page Hacker Revived Requires Restart

Adds a toolbar to edit and format the current page

No Caption

Hide the caption of Firefox

printplus Requires Restart

PDF export support by Gecko.
https://github.com/hATrayflood/printplus