SanRockstar Requires Restart

Music

RSS Icon in url bar

Add RSS icon into URL bar

Hide Option Pane Requires Restart

Provides ability to hide option panes.

Pic Zoom Requires Restart

Zoom in and out of any image on a page

IMEStatus Requires Restart

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

Tools > Options… for Linux

Moves Edit > Preferences to Tools > Options…

Restart Application Button

Restart Application Button lets you restart your Firefox and SeaMonkey application by a quick toolbar button click.

about:kittens Requires Restart

Baby cats and kittens in the about box...

No Caption

Hide the caption of Firefox

UI Text Overrider

Provides ability to override UI elements' label, tooltip text, etc.

Switch Message Colour Requires Restart

Adds a Toolbar-Button to Thunderbird to switch between the mails' original colouring and your user defined colouring.

Select like a Boss

Select link's text just like a regular text (like in Opera'12 browser) - Select like a Boss ;)

AntiLostFilter Requires Restart

Фильтр для конференций AUTO.RU

Elegant Scrollbar Cursors

Display helpful, informative cursors for scrollbars.

ZenbuShiitake Requires Restart

Track your shipment Requires Restart

Link to tracking sites. (mainly Japanese companies)

Disable About Something Requires Restart

Provides ability to disable "about:*" pages by the configuration.

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.

No Close Other Tabs Requires Restart

Removes "Close other tabs" context menu item.

Splash! (Compatibility Update) Requires Restart

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