Mozilla Firefox for Web Developers
Web Developer
You can disable elements, manage cookies, manipulate html, css, validate html, css
NoScript
Disable javascript, you can add/remove host on whitelist to trusted sites
iMacros
Why do the same all day, use a macro and see the browser do your job, fill forms, upload or download files, click some links, etc…
Documentation on http://wiki.imacros.net/Main_Page
Greasemonkey
User scripts execute extra javascript code on websites (Opera supports user scripts http://www.opera.com/browser/tutorials/userjs/using/)
// ==UserScript==
// @name Name of the script
// @namespace http://{url}
// @description description about this user script
// @include http://localhost/*
// @exclude http://localhost/admin/*
// ==/UserScript==
Documentation on http://diveintogreasemonkey.org/
Firebug
Something is wrong on your website? debug use firebug manipulate html, css and javascript
Firebug Lite (MSIE, Opera and Safari support)
FirePHP
For PHP developers you need include the FirePHPCore library on your project
<?php
FB::log('Log message');
FB::info('Info message');
FB::warn('Warn message');
FB::error('Error message');
?>
Integrate with you PHP framework:
BIGACE, CakePHP, CodeIgniter, Drupal, ExpressionEngine, Kohana, PEAR, PRADO, Smarty, Solar, Symfony, TYPO3, ZendFramework
Learn how to use FirePHP
FireFTP
Upload or download files, fireFTP open a new tab with a graphical interface, optional store accounts (user/pass/host)
TamperData
Manipulate request headers (POST and GET) good for testing the security of the project
HackBar
XSS, Base64 encode/decode, URL encode/decode, hashing (md5, sha-1, sha-256, rot13), etc…
Links to the Add Ons:
Web Developer (https://addons.mozilla.org/en-US/firefox/addon/60)
NoScript (https://addons.mozilla.org/en-US/firefox/addon/722)
iMacros (https://addons.mozilla.org/en-US/firefox/addon/3863)
Greasemonkey (https://addons.mozilla.org/eu/firefox/addon/748)
Firebug (https://addons.mozilla.org/en-US/firefox/addon/1843)
FirePHP (https://addons.mozilla.org/en-US/firefox/addon/6149)
FireFTP (https://addons.mozilla.org/en-US/firefox/addon/684)
Tamper Data (https://addons.mozilla.org/en-US/firefox/addon/966)
HackBar (https://addons.mozilla.org/en-US/firefox/addon/3899)