Web Developers are hungry for anything that makes their lives easier. That’s why IE may still have more overall users in the world, but amongst developers, Firefox rules. Not only is it a far better browser, but the extensions available can save you hours of wasted time and headaches. Here are the ones I highly recommend every web developer install right away.

Firefox Developer Extensions

Web Developer - The king of web development extensions. This single extension contains nearly every tool imaginable. If you’ve been building sites without this, you have been practically standing still. https://addons.mozilla.org/en-US/firefox/addon/60

Firebug - Debugging JavaScript is nearly impossible if you don’t have this extension. Without it you can only guess what’s wrong with your code. Also gives CSS info and lists everything a page loaded along with load time allowing you to spot spot what’s making pages drag. https://addons.mozilla.org/en-US/firefox/addon/1843

MeasureIt - Don’t just estimate how much further some part of your site needs to move to make it look right. Use this nifty extension and know exactly how many pixels you need to add. https://addons.mozilla.org/en-US/firefox/addon/539

ColorZilla - Quickly find out the color of anything on a page. Colorzilla is a well thought out color sampler with a host of options including a choice of color wheels. https://addons.mozilla.org/en-US/firefox/addon/271

Live HTTP Headers - Take the mystery out of HTTP headers with this extension creates a window that allows you to view them instantly as the page loads. https://addons.mozilla.org/en-US/firefox/addon/3829

Word Count Plus - Don’t count characters or words manually. That’s a stupid waste of time. This must-have extension gives you the word count and character count of any block of text you highlight. https://addons.mozilla.org/en-US/firefox/addon/4718

Y slow - Why is your site not as fast as it could be? This extension gives you more detail than you ever wanted to know about your sites performance by grading your A through F on a list of optimization points. https://addons.mozilla.org/en-US/firefox/addon/5369

Fireform - Don’t you get tired of filling out the same form for testing over and over again? Fireform to the rescue. Simply fill out the form once, then tell Fireform to remember it. https://addons.mozilla.org/en-US/firefox/addon/3193

SEO Quake - Once you get that new site launched what good does it do anyone languishing at the bottom of the search results pile. SEO Quake gives you a number of tools to help optimize your site to reach its search engine placement potential. https://addons.mozilla.org/en-US/firefox/addon/3036

Cacheviewer - During development if you don’t see what you expected to on a page, your first stop is often the cache. Is the browser respecting your cache settings? Did you forget to tell it what to cache? With the Cacheviewer extension you can see what your browser is holding onto, when it was last fetched, etc. It’s the same information as Firefox’s “about:cache” but a) you don’t need to remember the syntax and b) this is much easier to read. https://addons.mozilla.org/en-US/firefox/addon/2489

Copy Plain Text -Ever highlighted some text on a site then tried to paste it somewhere only to find that you accidentally copied all of the links and font settings with it? The only way around this was to paste into a flat text editor then copy it again. Now you can skip that step with this plug-in. One annoyance, however, last I checked the keyboard shortcut for this tool is duplicated by the Web Developer extension which takes precedence. To use the feature, you need to right-click or select it from the main menu. Hopefully Jeremy will address this one day. https://addons.mozilla.org/en-US/firefox/addon/134

Google Toolbar - Some of the Google Toolbar functionality is duplicated in SEO Quake above but I still recommend installing both. Not only does it help to see what others see (GT is often installed by non-developers as well), but it instantly tells you a site’s Google rank. This magic number can typically tell you if you’re handling your optimization as well as you should be. https://addons.mozilla.org/en-US/firefox/addon/6249

Split Browser - Makes comparing websites a snap. It’s one of those tools you don’t think you need until something doesn’t match between dev and production. https://addons.mozilla.org/en-US/firefox/addon/4287

Recently mentioned but worth including:

Pinger - a nifty link checker that follows URLs on the current page and alerts you to those responding with 404’s. Very useful for quickly checking pages that have been up for a while. https://addons.mozilla.org/en-US/firefox/addon/10201

URL Flipper - ever need to increment or decrement your way through a bunch of related pages? This extension will become your best friend. I stumbled across it accidentally but I don’t know how I did without it. Personally I use it to check on content accessible by id numbers that are in a series. Instead of changing the id manually, I just use a keyboard shortcut and instantly move to the next id. https://addons.mozilla.org/en-US/firefox/addon/3572

ShowIP - Displays the IP address (or addresses) of the page you are viewing. Handy for those miserable DNS change days when the only difference between two sites is where they are hosted. This way you know which server you are looking at instantly. Also sports quicklinks to common tools like whois and traceroute. https://addons.mozilla.org/en-US/firefox/addon/590

ScreenGrab - I mentioned Abduction in a previous post which also grabs a snapshot of the current page or section of the page. I used to love Abduction, but then the developer committed a terrible sin. He didn’t update the extension for 3.5 quickly enough. I take screengrabs several times a day and going back to the clunky system method was driving me crazy. I found ScreenGrab to use while I waited for Abduction to catch up and found that I liked it better. Fundamentally they both work but ScreenGrab gives you more options right in the menu. If you use any other screengrab extension try this one for comparison. I’d be interested to hear what you think. https://addons.mozilla.org/en-US/firefox/addon/1146

QuickRestart - Why isn’t there a restart option above Quit in the Firefox menu? Well there can be now. Restart has become a common step after adding in plug-ins or finding that JavaScript has gone haywire thanks to some bozo’s webpage. https://addons.mozilla.org/en-US/firefox/addon/3559

If you know of other essential extensions that I have overlooked, feel free to post them to the comments area below.