A great list of tools I use at work to support web developers and designers troubleshoot issues with their websites.
Protect your privacy. See who's tracking your web browsing and block them with Ghostery.
The User Agent Switcher extension adds a menu and a toolbar button to switch the user agent of a browser.
The Web Developer extension adds various web developer tools to the browser.
Advanced Eyedropper, Color Picker, Gradient Generator and other colorful goodies...
IE Tab - an extension from Taiwan, features: Embedding Internet Explorer in tabs of Mozilla/Firefox...
YSlow analyzes web pages and suggests ways to improve their performance based on a set of rules for high performance web pages.
http://yslow.org is the official open source website.
Show the IP address of the current page in the status bar. It also allows querying custom information services by IP (right click) and see location and avaiable vouchers for shopping sites. Additionally you can copy the IP address to the clipboard.
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.
A Statusbar with speed, percentage, time and loaded size (similar to Opera's one)
Lets you load pages in IE with a single right-click, or mark certain sites to *always* load in IE.
View and manage downloads from a tidy statusbar - without the download window getting in the way of your web browsing.
Thanks Tekzilla for your awesome review! Click here to see their video: http://youtu.be/BUDqWrJ-Vao