Below is the list of 50 firefox addons that makes your firebox browser experience a better one. Adblock Plus - It is one of the important firefox addon that blocks advertisements to appear on any webpage.

Aging Tabs – Makes unused tabs fade with age and highlights the selected tab.

All-in-One Sidebar - Sidebar control with award-winning user experience.

Auto Copy - Copies selected text to the clipboard automatically. Like Linux or mIrc.

AutoPager - AutoPager is a firefox/mozilla extension that autoloads the next page in background.

Better GCal - Enhances Google Calendar with a compilation of user scripts and styles. All scripts copyright their original authors. Click on the script homepage in the Help tab for more information.

Better Gmail 2 – Enhances Gmail with a compilation of useful features written by Greasemonkey user script developers. All scripts copyright their original authors. Click on the script homepage in the Help tab for more information.

Better YouTube – A compilation of useful Greasemonkey user scripts for YouTube. All scripts copyright their original authors. Click on the script homepage in the Help tab for more information.

ColorZilla - Advanced Eyedropper, ColorPicker, Page Zoomer and other colorful goodies

Cooliris – Cooliris (formerly PicLens) transforms your browser into a full-screen 3D Wall for searching, viewing and sharing the Web.

CustomizeGoogle - Enhance Google search results and remove ads and spam.

Delicious Bookmarks – Access your bookmarks wherever you go and keep them organized no matter how many you have.

DownloadHelper - Download videos and images from many sites. It is the best tool to

download videos from YouTube etc .

FEBE – Backup your Firefox data

Fire.fm - Get your daily music fix from Last.fm.

Firefox Universal Uploader (fireuploader) – Provides an user friendly interface to upload files to various websites eg. Box.net, Flickr, Youtube, Picasa, Facebook

FireFTP – FTP Client for Mozilla Firefox.

FlashGot – Enables single and massive (”all” and “selection”) downloads using the most popular external download managers for Windows, Mac OS X, Linux and FreeBSD.

FoxClocks – Displays local times around the world in the statusbar/toolbar. Supports virtually all time zones.

FoxyProxy - FoxyProxy – Premier proxy management for Firefox

FoxyTunes - Control any media player from Firefox and more…

gDocsBar – Perfect companion for Google Docs. 

Gmail Manager – Gmail accounts management and new mail notifications.

GmailSpace -Use your Gmail account space for file storage. Enables uploading/downloading of folders.

GooglePreview - Inserts web site previews in Google and Yahoo search results.

Greasemonkey – A User Script Manager for Firefox

IE Tab – Enables you to use the embedded IE engine within Mozilla/Firefox.

Master Password Timeout – Locks the master security device after a predefined period of inactivity

NoScript - Extra protection for your Firefox: NoScript allows javascript, Java (and other

plugins) only for trusted domains of your choice (e.g. your home-banking web site).

Password Exporter - Export and import the saved passwords.

PC Sync 2 Synchronisation Extension – Enables PC Sync 2 synchronization support.

PDF Download – Allows you to choose what to do with a PDF file: download it, view it with an external viewer or view it as HTML.

Perspectives - A secure way to verify encrypted websites and bypass security warnings

ProfileSwitcher – Adds profile name to status bar tooltip and options to launch other profiles 

Read it Later – Save pages to read later, then bookmark.

ScrapBook – Helps you to save Web pages and organize the collection.

Screen grab! – Saves a web-page as an image.

ScribeFire – A full-featured blog editor that integrates with your browser and lets you easily post to your blog.

Twitbin – Twitbin is a tool that allows you to interact with your twitter friends and followers right from your browser sidebar.

Yahoo! Mail Notifier – This extension notifies you when new messages arrive in your Yahoo mailbox.

Flashblock - The plugin blocks flash from running. It acts on all sites by default, but lets you set ‘whitelists’ of sites that can use flash, such as youtube. For blocked sites (those not on the whitelise) you get a window of the right size on the screen, and a ‘play’ button you can click if you want to load the animation. Here is an opera version.

Fasterfox - A bunch of tweaks to speed up firefox simply without manually tuning the registry parameters. Can be set to exceed the RFC specs if you want. Also provides a page load timer in the bottom right which is I like. See how much of a change you get after installing flashblock

Autocomplete Manager – When you type into the default firefox location bar, you get ‘autocomplete’ suggestions based on the part of the URL you typed. This plugin enhances that so it automatically searches on bookmarks, and even web page titles from your history. If you keep a long enough history, it could almost render your bookmarks obsolete.

Firebug – Essential for anyone who does web development. Install it, then for a page you want to analyze click Tools/Firebug. Click ‘inspect’ and point your mouse at any part of a web page and it’ll show a breakdown of the HTML in that section only, and let you modify the source ‘live’ to test fixes. Great for showing how web pages are composed, and it’s a much nicer alternative to a full ‘view page source’ option. Firebug and the inspect facility can be added as icons to your toolbar, so it doesn’t clutter up yourbrowser out of the box. There is also a YSlow plugin that you can add after installing firebug to perform performance analysis on web pages. FoxEar – Essential internal tool that gives you a sidebar to interface into DogEar.

Fast Video Download – It downloads videos from YouTube. You get an icon in the bottom right that you click when you’re on a page with embedded video, and it lets you save it.

Remove It Permanently - (RIP) RIP lets you right click on any section of a web page (Such as a sidebar or advert) and specify that it’s removed from all futuring rendering of the page. By using this carefully you can reclaim a lot of your browser screen area.

PDF Download – helps download the PDF documents