
If you're reading this, it more than likely means you're rather intelligent. Which would also mean that you're not using Internet Explorer. If so... then this is for you.
The following is a list of Firefox extensions that I frequently use. Some just make browsing easier in general... but many make graphic design, coding and getting things to work in IE much easier. In particular, the first two are must-haves. Feel free to mention your own useful extensions or add-ons in the comments section.
Colorzilla
gives you an eyedropper and other tools to gather color information. incredibly useful.
Web Developer
adds a menu and toolbar with various web developer tools (outline elements, view source, validation, element size and order, color eyedropper, etc.).
IE Tab
enables you to use the IE engine within a firefox tab.
TabPreview
get a thumbnail view of a page when you hover over its tab.
NukeAnything
remove any element on a page via the context menu.
Duplicate Tab
allows you to duplicate tabs or merge windows.
Tabbrowser Preferences
enhances control over tabbed browsing.
Bookmarks Synchronizer
connect to a server and synch your bookmarks across multiple computers. also recommended is
FoxMarks, which will keep your bookmarks on their server instead of needing your own.
Plain Text Links
treat selected plain text urls as links, right click to open.
Linky
open/download/validate multiple links and pictures in tabs or windows.
TabFX
more nifty tab browsing enhancements.
Open link in...
adds more opening options to the context menu for links and images.