...listed in order of usefulness/importance.
Firefox Add-Ons (Any OS)
- Greasemonkey
- Allows the way a webpage displays to be customized using small bits of JavaScript.
TIP: Find Scripts. - Google Toolbar
- Search right from the toolbar, make custom buttons, use Autofill to never type your address or credit card number again.
REQUEST: Could someone please design buttons to search ADS and SIMBAD! - Drag and Drop Upload
- Never browse for a file to upload or attach, instead drag files from Finder into file upload fields to copy the path.
- Tab Mix Plus
- Enhances tab browsing capabilities with such features as duplicating tabs, controlling tab focus, tab clicking options, undo closed tabs and windows, plus much more.
TIP: I prefer this addon's Session Manager over the one built in to Firefox. - Colorful Tabs
- Adds color to tabs to make them easier to distinguish.
- Download Statusbar
- Replaces Downloads Window with a status bar located at the bottom of the browser window.
- Leech Block
- Give yourself time limits at websites where you waste time (e.g., Facebook, Google Reader, Flickr).
TIP: I've found 5 minutes per hour to do the trick. - Better Gmail 2 for new Gmail and Better Gmail for the old interface
- A comprehensive suite of Greasemonkey scripts for Gmail including skins, saved searches, keyboard macros, secure access, attachment icons, attachment reminders, label colors, signature floating and more.
- Quick Restart
- Adds a "Restart Firefox" item to the Tools menu and a toolbar button.
- Better Flickr
- Compilation of Greasemonkey scripts adding optional extra features to flickr.
- Menu Editor
- Rearrange or remove menu items from the main context menu (right-click menu) and main menubar (File Edit View etc.).