1. CSSViewer

What if you want to see CSS parameters of any specific element in a web page, it’s where CSSViewer comes in. You can disable or enable it by simply clicking the toolbar icon.

2. Code Cola

Code Cola is a chrome extension to editor online pages’ style visibility. It helps visual designer, interactive designer, web site operator and other peoples modify the online pages quickly and easily.

3. Live CSS Editor

If you want to see the immediate results while you are changing the CSS, this extension provides a text box on any HTML page so that you can write CSS freely and preview the results.

4. CSS Reloader

CSS Reloader is a chrome extension that allows you to reload CSS without reloading the whole page.

Here are the 6 must have Google chrome extensions.

1. Chrome SEO

The Google Chrome SEO Extension provides easy access to Search Engine Optimization Tools that can help you with Competitive Analysis, Keyword Research, Backlink Checks, PageRank Checks and other daily SEO tasks.

2. SEO Site Tools

Using this chrome extension you can check On-Page / External metrics, Social Media info, PR / numbering on Yahoo, Bing, Google SERPs.Extends WMT, YSE and GA with metrics.

3. SEO & Website Analysis

SEO report is an extension for Google Chrome™ done by WooRank that provides a very deep SEO report for any given website.

4. SEO Status Pagerank/Alexa Toolbar

SEO Status is lightweight. It will check the Google Pagerank (PR) & Alexa rank for every page. Using this will increase your Alexa.

5. SeoQuake

Displays the Google PageRank, Alexa rank and other SEO parameters of any webpage, highlights nofollow links, text density, check and compare urls.

6. Keyword Eye

The tool will return keyword ideas for a keyword or URL in a cloud format where search volume is indicated by the size of the keyword and competitiveness by colour.

Here, we have compiled a list of 15 most useful and best Chrome extensions for web developers and designers. Don’t hesitate to try all of them and if you already have used any of it don’t forget to share your experience with us.

1. Speed Tracer

Speed Tracer is a tool to help you identify and fix performance problems in your web applications. It visualizes metrics that are taken from low level instrumentation points inside of the browser and analyzes them as your application runs.

2. Eye Dropper

Eye Dropper and Color Picker extension which allows you to pick color from any webpage or from advanced color picker.

3. Firebug Lite

Firebug Lite is a tool for web developers, that allows you to edit, debug, and monitor CSS, HTML, and JavaScript live in any web page.

4. Chrome SEO

The Google Chrome SEO Extension provides easy access to Search Engine Optimization Tools that can help you with Competitive Analysis, Keyword Research, Backlink Checks, PageRank Checks and other daily SEO tasks.

5. Pendule

Pendule displays linked and embedded style sheets of the current page in a new tab.

6. Aviary Screen Capture

Take a screenshot of any webpage and edit it directly in your browser with Aviary.com applications. Plus convenient access to the Aviary website and tools.

7. Resolution Test

Resolution Test changes the size of the browser window for developers to preview their websites in different screen resolutions. It includes a list of commonly used resolutions as well as a custom option for you to input your own.

8. PlainClothes

This extension styles — or rather “unstyles” — the web. Just imagine: text is black, backgrounds are white, unread links are blue, visited links are purple, all links are underlined. Or any other colors you like.

9. Snippy

Snippy allows you to grab snippets of web pages, save them for future use and upload them to Google Docs.

10. FlashBlock

Flashblock is an extension for the Google Chrome that blocks all Flash content from loading. It then leaves placeholders on the webpage that allow you to click to download and then view the Flash content.

11. IE Tab

Use Internet Explorer to display web pages in a Chrome tab. Some sites can only be displayed using IE, and with this extension you can now see those sites without leaving Chrome.

12. Validity

Validity can be used to quickly validate your HTML documents from the address bar.

13. BuiltWith Technology Profiler

BuiltWith is a web site profiler tool. Upon looking up a page, BuiltWith returns all the technologies it can find on the page.

14. MeasureIt!

Draw out a ruler that will help you get the pixel width and height of any elements on a webpage.

15. LastPass

LastPass is a free online password manager and Form Filler that makes your web browsing easier and more secure.

Here i have collected top 10 Firefox 3.5 compatible themes (add-ons) for you, so that you can start customizing your browser. You can download the add-ons by clicking the links given below and can change the theme after installing them from ‘Tools’ menu.

1. Vista-aero

The most IE8-like theme with Vista Aero style!

2. Silvermel

This theme is a modification from the fantastic theme Charamel.

3. Chromifox Extreme

An Extreme coat of Chrome for Firefox.

4. Strata40

This theme aims to give the user an interface as close to the new Firefox 4 mockups as possible.

5. Office 2007 Black

A theme based on the Office 2007 Black colours.

6. Walnut2

Walnut2, based on icons from art.gnome.org. Includes support for help, inspector, downloadstatusbar, downloadmgr, calendar, quicknote, offline, toolbarext. and many other extensions.

7. Curacao

An exotic yet exquisite alliance of blue and brown.

8. Foxdie

Turns Firefox into a Safari.

9. Red Cats

Turn your Firefox into Firecat and enjoy browsing in the furry company. The theme is also available in green flavor.

10. Chromifox Extreme Green

Chromifox is a dark and deep green theme for Firefox on Windows, Linux, and Mac OS X, inspired by the appearance of the Google Chrome browser.

Here goes the list of plugins:

1. TwitterFox

TwitterFox is a Firefox extension that notifies you of your friends’ status on Twitter.

TwitterFox Plugin

2. TwitterBar

Post to Twitter from your address bar.

TwitterBar Firefox Plugin

3. Twitter Line

Twitter Line is an extention for Firefox that displays your Twitter time line on the toolbar as like as a head line (or ticker).

Twitter Line Firefox Plugin

4. Power Twitter

Power Twitter adds features to the Twitter Web interface.

Power Twitter Firefox Plugin

5. Twitter Search

This search plugin gives you quick access to the real-time Twitter search.

Twitter Search Firefox Plugin

6. StockTwits

Install and magically turn StockTwits tagged tickers on twitter.com into links back to stocktwits.com so you can easily catch up with the latest conversations.

StockTwits Firefox Plugin

7. Twitzer

Twitzer is a Firefox extension which lets you post text longer than 140 characters on Twitter.com.

Twitzer Firefox Plugin

8. InstantTweets

Instantly send pages, pictures and tweets to Twitter from any where on the web.

InstantTweets Firefox Plugin

9. Tweecious

Listening to your twitter feed and submitting all the links to your delicious account.

Tweecious Firefox Plugin

10. TwitKit

TwitKit is a Twitter sidebar for Firefox. It has many features that other clients are missing – so come on and try it already!

TwitKit Firefox Plugin

11. Twitbin

Twitbin is a firefox extension that allows you to keep up with all of your Twitter conversations right from your browser sidebar. Send messages, receive messages, share links, and more from Twitbin, the best twitter addon for firefox out there.

Twitbin Firefox Plugin

12. DashBlog

DashBlog lets you quickly collect videos, images, text/quotes, songs and screen-captures from any web page and publish them to your blog (word press, blogger/blogspot, tumblr) and/or twitter.

DashBlog Firefox Plugin

13. Social Whale Extension

Create short URLs for use with twitter or any other service with just one click. Additionally you can upload images using the twitpic.com service.

Social Whale Extension

14. TwitThat

Post current page to twitter via twitthat.com.

TwitThat Firefox Plugin

15. TwittyTunes

Allows to post your currently playing songs to Twitter with a click. As a bonus, you can also post the websites you’re visiting, videos you’re watching and more!

TwittyTunes Firefox Plugin

16. Tweetstalk

The simple way to stalk Twitter users without having to follow them.

TweetsTalk Firefox Plugin

17. Yoono – Socialize Your Browser

All your social networks and instant messaging in one easy to use browser sidebar. Get all your friend updates, update your status and share stuff easily across Facebook, MySpace, Twitter, and more – all at once! Simplify your online social life.

Yoono Firefox Plugin

I decided to list the most useful and popular Firefox extensions for Gmail

1. Better Gmail 2

Add useful extra features to Gmail, like hierarchical labels, macros, file attachment icons, and more.

Better Gmail 2 compiles the best Greasemonkey user scripts for Gmail into a single package. All scripts copyright their original authors. Click on the script homepage in the About tab for help and more information. Only compatible with the new Gmail interface.

Better Gmail 2

Main Site | Download

2. GTDInbox

GTDInbox is an addon for Firefox that transforms Gmail into a powerhouse of productivity and manageability. GTDInbox gives you a better inbox.

GTDInbox

Main Site | Download

3. DragDropUpload

This extension lets fill an upload input of a form using the drag and drop service from the system. Just drop the file into the input box and then send it.

DragDropUpload

Main Site | Download

4. Gspace

This extension allows you to use your Gmail Space (7.3 GB and growing) for file storage. It acts as an online drive, so you can upload files from your hard drive and access them from every Internet capable system.

Gspace

Main Site | Download

5. Gmail Manager

The original Gmail notifier for multiple accounts. Allows you to manage multiple Gmail accounts and receive new mail notifications. Displays your account details including unread messages, saved drafts, spam messages, labels with new mail, space used, and new mail snippets.

Gmail Manager

Main Site | Download

6. Gmail Skins

Gmail Skins is an extension that tries to make your Gmail experiance a little better.

Gmail Skins

Main Site | Download

7. GPhotospace

GPhotospace is the fastest way to share photos online. This free photo album builder works elegantly with Firefox and Gmail. Use your existing Gmail account or create a new one for use with GPhotoSpace. Create any number of photo albums, store them and share them instantly.

GPhotospace

Main Site | Download

8. Gmail Contact Book

With this addon,you can now easily pick your contacts from the [Contact Book] by click the little book beside To,CC,BCC Boxs.

Gmail Contact Book

Main Site | Download

9. Remember The Milk

Remember The Milk for Gmail is a Firefox extension that allows you to manage your tasks in Gmail (complete, postpone, and edit tasks), add new tasks (and connect them with your emails, contacts, and Google Calendar events), automatically add tasks for starred messages or specific labels, and much more!

Remember The Milk

Main Site | Download

10. Easy Job Application

Easily send job applications using Gmail in websites like Craigslist.

Easy Job Application

Main Site | Download

11. WebMail Notifier

WebMail Notifier checks your webmail accounts and notifies the number of unread emails.

WebMail Notifier

Main Site | Download

12. Todoist

Todoist is a task manager that’s useful, fast and easy to use. We currently manage millions of todos for thousands of people.

Todoist

Main Site | Download

13. WiseStamp Email Signatures

WiseStamp a Firefox extension enables you to easily customize & add personalized email signatures on any webmail service (Gmail ,Yahoo Mail ,AOL mail, Hotmail, Google Apps…)

WiseStamp Email Signatures

Main Site | Download

14. WebMail Ad Blocker

More screen space for your messages! Yahoo Mail, Hotmail, and Gmail advertisements take up a lot of space even if they get blocked by other addons because they leave unused empty space.

WebMail Ad Blocker

Main Site | Download

15. Email This! Bookmarklet Extension

Email This! will send your recipient the link, title, & highlighted text of the page you are viewing using GMail.

Email This! Bookmarklet Extension

Main Site | Download

16. gTalk Sidebar

Can’t use gmail? Don’t have time to install Gtalk? Want a simple solution? Then try using gTalk from your sidebar!

Main Site | Download

17. FreeAccess Plus!

Bypass filter of del.icio.us, Flickr, Technorati.com, FriendSter.com, livejournal.com and MySpace.

FreeAccess Plus!

Main Site | Download

18. iFox Smooth

A minimal, compact, elegant theme for firefox.

iFox Smooth

Main Site | Download

If you want more firefox extensions for Gmail visit Mozilla.org