Fast Close Tabs Requires Restart

Closing the window closes the active tab instead of the window.

ACColorPicker

A full featured color selector tool, to work with colors, and easily find the colors you want.
很方便色取色器，可以页面上直接取色，然后再对颜色进行进一步的调整

Disable about:config Requires Restart

Disable about:config feature of Firefox and Thunderbird.

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

Switch Message Colour Requires Restart

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

UI Text Overrider

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

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

Disable About Something Requires Restart

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

Track your shipment Requires Restart

Link to tracking sites. (mainly Japanese companies)