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新同文堂 (New Tong Wen Tang)

NewTongWenTang is a tool to switch display Chinese content between traditional and simplified glyphs (中文繁簡體互轉工具)

Rated 4 out of 5 stars (96)
39,042 users

Classic Toolbar Buttons No Restart

'Classic Toolbar Buttons' add-on restores old toolbar button ui (known from Fx 4-7s small view, Fx 4-12s large view & Tb 5-14) for current Firefox, Thunderbird and Seamonkey versions on Windows.

Beta builds on versions page!

Rated 5 out of 5 stars (144)
38,713 users

Minimize On Start and Close

A remake of the MinimizeToTray-extension made to fit the Windows 7 taskbar. Instead of minimize the window to the tray it minimize it to the taskbar. It can minimize on startup, when the window is closed and/or when the esc key is pressed.

Rated 4 out of 5 stars (93)
38,019 users

Disable Add-on Compatibility Checks No Restart

Reinstates the extensions.checkCompatibility preference without respect to the current application version.

Rated 4 out of 5 stars (92)
37,905 users

Folderpane Tools

Allows for customization of the folder pane. Accounts can be rearranged and the startup folder can be chosen.

Rated 4 out of 5 stars (121)
36,496 users

Nightly Tester Tools

Useful tools for the nightly tester.

Rated 4 out of 5 stars (189)
36,186 users

Clean Links No Restart

Converts obfuscated or nested links to genuine clean links.

Eg: http://somesite.com/?to=www.example.comhttp://www.example.com/

Rated 4 out of 5 stars (95)
36,091 users

Copy Plain Text 2

Copies text without formatting

Rated 5 out of 5 stars (58)
34,245 users

Stationery

Extension to mimic Outlook Express Stationery.
Allow you to use HTML files as templates for mail. Also allow custom template in replies or forwarded mail!

Rated 4 out of 5 stars (105)
33,208 users

Display Mail User Agent

Displays icon for user agent of received mails.

Rated 4 out of 5 stars (103)
32,364 users

AttachmentExtractor

Extracts all attachments from selected messages and then can delete, detach or mark-read.

Rated 4 out of 5 stars (167)
32,232 users

Tiny JavaScript Debugger

TinyJSD is a JavaScript debugger for privileged code running Mozilla products like Firefox, Thunderbird, SeaMonkey. It serves to debug the application as well as extensions written in JavaScript.

Rated 4 out of 5 stars (5)
31,640 users

Contacts Sidebar Featured

Displays the address books in a sidebar in Thunderbirds 3-pane-window and can be toggled with the F4 key or a toolbar button.

Visit my Contacts Sidebar site for recent versions and news.

Rated 4 out of 5 stars (272)
31,511 users

Clippings

Save frequently-entered text for pasting later.

Rated 4 out of 5 stars (166)
31,112 users

Font Finder

FontFinder is created for designers, developers and typographers. It allows a user to analyze the font information of any element on a page, copy any piece(s) of that information to the clipboard, and perform inline replacements to test new layouts.

Rated 4 out of 5 stars (67)
30,483 users

Zindus

Google and Zimbra contact sync for Thunderbird. (TB 24 and above NOT supported)

Rated 4 out of 5 stars (206)
30,249 users

Addressbooks Synchronizer

Synchronizes selected addressbooks with other instances of thunderbird
using ftp/webdav/imap servers

Rated 4 out of 5 stars (57)
29,653 users

Mail Redirect Featured

Allow to redirect (a.k.a. "bounce") mail messages to other recipients.

Rated 4 out of 5 stars (123)
28,955 users

Firesizer

Allows you to resize the window to specific dimensions.

NOTE: Users of Firefox 29 and above must install "The Addon Bar" extension to use this, as Firesizer uses the add-on bar that has been removed in Firefox 29.

Rated 4 out of 5 stars (124)
28,911 users

Display Quota

This extension will display the current status of your IMAP quota in thunderbird's statusbar and will warn you when you reach a configurable limit...

Rated 4 out of 5 stars (28)
27,174 users