Add-ons

AutoPager by Wind Li

AutoPager automatically loads next pages when you reach the end of a page. It works on a ton of sites,Google,Yahoo..
It works well with most other add-ons adblock plus, WOT and most of the greasemonkey scripts.
You can also try AutoPagerLite.

Restartless Restart by Erik Vold

This 15KB restartless add-on will add a "File" -> "Restart" menu item and a ctrl/cmd + alt + r hotkey to restart Firefox or Seamonkey.

Ruler Bar by Piro (piro_or)

This appends a ruler to the mail composition window.

Extension List Dumper by Sogame

This extension adds a button ("Dump list") to the Add-ons window. When this button is pressed, a new window is opened with the list of installed extensions, themes or plugins...

SearchWith by soyapi

Search selected text with various search services...

Restart Thunderbird by Briks Software, David McNamara

Restart Thunderbird with ease.

中止ボタンがしいたけに見えて困る by Hadakadenkyu

Huh, you said the stop button looks like shiitake? No way, you must be tired.

Old Japanese Paper mac by Ratouschnikova