Wappalyzer is a browser extension that identifies software on websites.
This extension prevents Google, Yahoo and Yandex search pages from modifying search result links when you click them. This is useful when copying links but it also helps privacy by preventing the search engines from recording your clicks.
Quickly and easily switch between popular user-agent strings.
Debug Flash/SWF files on the web. Edit properties and inspect elements on the fly. View log output inside the extension. Run AS3 code against the active SWF. Access assets with the Explorer. View AMF calls and Shared Objects and much much more...
Color tools for web development.
Color picker and eyedropper + saving colors and trying out colors with drag and drop.
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.
Collector's Note "Easy and fast to use - use the eyedropper tool OR highlight and right click. And it gives me exactly the info I need: font stack vs. rendered font, size, color, spacing - without overloading me with info I don't need or want to search through" Open source (GNU)
this add-on simulates japanese mobile device.
this add-on support DoCoMo, Au(KDDI) and SoftBank device.
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 Firefox 23+, you need 0.958 (under review)
CodeBurner is a Firefox add-on that integrates with Firebug, to extend it with reference material for HTML and CSS.
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.
Display the Google PageRank, Alexa rank, Compete ranking and SEOmoz Linkscape mozRank anywhere in your browser, along with fast keyword density analyser, keyword/nofollow highlighting, backward/related links, canonical links, WHOIS, robots and more.
Extracts all links from web page, sorts them, removes duplicates, and displays them in a new tab for inspection or copy and paste into other systems.
Firebug extension to view which CSS rules are actually used.
Collector's Note (fr) Gère les @import. Looks like doens't support UTF-8 (i.e. display of Chinese characters)