HTML and CSS Reference
Validator and Debugger Plug-ins
Browsers can also be extended with additional functionality by installing developer plug-ins, many of which are
There are numerous add-ons for Firefox that can be useful for developers . For example, HTML Validator is an
extension that adds HTML validation inside Firefox . It clearly indicates the number of markup errors as an icon in
the status bar when browsing. Live HTTP Headers displays HTTP headers of a page and while browsing . FireFTP
is a free, secure, cross-platform (S)FTP client for the browser . The User Agent Switcher extension adds a menu
and a toolbar button to switch the user agent of the browser . The IE Tab extension supports Internet Explorer
rendering from IE6 to IE9, which can be useful for testing purposes . The Web Developer extension adds various
web developer tools to a browser, such as the option to disable certain styles or display CSS by media type . One of
the most comprehensive developer add-ons for Firefox is Firebug . It integrates several development tools to the
Figure 11-10. Firebug in action
Some of these Firefox tools are also available under Chrome (for example, Firebug , Web Developer ), and
the ones that do not have a Chrome version have their equivalents for Chrome (such as IE Tab ). There are many
other developer tools under Chrome , such as W3C HTML5 & CSS3 Validator , Validity that validates the markup
from the address bar (or with hotkeys) , colorPicker , XML Tree , Resolution Test , just to mention a few.
Testing Web Pages in Text Browsers
Testing a web site in text browsers such as Lynx  is the best method to check information availability without styles
and graphics 4 as well as accessibility. Properly designed web content remains usable in text browsers (Figure 11-11 ),
while a large share of web sites do not.
4 Lynx cannot display nontext contents by default, but external programs can be launched from Lynx such as image viewers
or video players.