HTML Validator is a Mozilla extension that adds HTML validation inside Firefox and Mozilla. The number of errors of a HTML page is seen on the form of an icon
For Online HTML 5 validation, you need 0.962
Random Agent Spoofer No Restart
Rotates complete browser profiles ( from real browsers / devices ) at a user defined time interval. It includes many extra privacy enhancing options
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.
Proxy Switcher No Restart Featured
Access to the complete Firefox's proxy settings right from a toolbar panel
User-Agent Switcher No Restart Featured
Quickly and easily switch between popular user-agent strings.
A developer tool for interacting with web services and other web resources that lets you make HTTP requests, set the entity body, and content type. This allows you to interact with web services and inspect the results...
Extended Statusbar No Restart
A Statusbar with speed, percentage, time and loaded size (similar to Opera's one)
this add-on simulates japanese mobile device.
this add-on support DoCoMo, Au(KDDI) and SoftBank device.
FirePHP enables you to log to your Firebug Console using a simple PHP method call.
Not using Firebug 1.9+ on Firefox 8+? See http://firephp.org/
HTTP/2 and SPDY indicator No Restart
An indicator showing HTTP/2 and SPDY support in the address bar.
Get SEO metrics while you surf! For each page you visit, see metrics like Domain and Page Authority, analyze links, expose page elements, and access other SEO tools. Next version will be for both Firefox and Chrome. Stay tuned!(This is version 2.6.5)
Classic Toolbar Buttons No Restart Featured
'Classic Toolbar Buttons' add-on restores old toolbar button ui (known from Fx 4-7s small view, Fx 4-12s large view & Tb 5-14) for current Firefox, Thunderbird and Seamonkey versions on Windows.
Beta builds on versions page!
1) Capture an page or just a specific region.
2) Adds a right click option to take screen shots of an entire web page or just part of a web page to save as an image.
A must have tool for Web Developers and Testers to Manage and monitor web cookies.
Export / Backup
Import / Restore
Available in English, French, Spanish, German and Italian languages.
about:addons-memory No Restart
Adds an about:addons-memory page that details add-on memory usage
Font Finder Featured
FontFinder is created for designers, developers and typographers. It allows a user to analyze the font information of any element on a page, copy any piece(s) of that information to the clipboard, and perform inline replacements to test new layouts.
Disable WebRTC No Restart
WebRTC leaks your actual IP addresses from behind your VPN, by default.