As of Firefox 33, Venkman *no longer works*, as the APIs which it needs have been removed.
ImportExportTools Requires Restart
Adds some tools to import and export folders and messages
SQLite Manager Requires Restart
Manage any SQLite database on your computer.
Fight the text ads! Element Hiding Helper is a companion extension for Adblock Plus meant to make creating element hiding rules easier.
If you are the kind of person who likes to have total control over every aspect of your downloads, "Download Status Bar" is the add-on you are looking for.
Ad Blocker lets you block all ads, tracking & malware from the web world. It is an effective solution to browse the web without offensive and annoying ads you hate to see.
Provider for Google Calendar Requires Restart
Allows bidirectional access to Google Calendar
Auto Resize Image Requires Restart
Resizer for inline and attachment images (JPEG, PNG, BMP and GIF image formats).
All platforms are supported (Windows, Linux and Macintosh).
By blocking annoying ads and nosy trackers, adaware ad block nearly doubles your browsing speed! And with the most robust antivirus-level cloud-scanning technology of any ad blocker on the market, you’ll be safe from the latest cyber-threats.
QuickNote Requires Restart
A simple note-taking extension.
MinimizeToTray revived Requires Restart
Minimizes windows into the system tray.
UnMHT allows you to view MHT (MHTML) web archive format files, and save complete web pages, including text and graphics, into a single MHT file in Firefox/SeaMonkey.
Font Finder Requires Restart
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.
'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.
Beta builds on versions page!
Copy Plain Text 2 Requires Restart
Copies text without formatting
ProfileSwitcher Requires Restart
It adds some options to launch easily other profiles and the Profile Manager.
"Restart" menu and button, with configurable shortcut key.
FoxClocks shows times around the world - or just your local time - at the bottom of your browser. It deals with daylight saving time so you don't have to.