Specificity is a mechanism within the CSS cascade that aids conflict resolution. The concept of specificity states that when two or more declarations that apply to the same element, and set the same property, have the same importance and origin, the declaration with the most specific selector will take precedence.
Specificity Calculator isn't a CSS validator. If you enter invalid selectors it will return incorrect results. For example, the negation pseudo-class may only take a simple selector as an argument. Using a psuedo-element or combinator as an argument for :not() is invalid CSS3 so Specificity Calculator will return incorrect results.
Responsive Measure is a simple script that allows you to pass in a selector (ideally the container where your primary content will go) which generates the ideal font size needed to produce the ideal measure for your text.
Firefinder is an add-on to Firebug, to help find HTML elements matching chosen CSS selector(s) or XPath expression. Type in desired filter and view the results.
CSS3 PIE is a .htc file that faithfully recreates css3 styling in early versions of internet explorer. Simply adding "behavior: url(path/to/PIE.htc);" at the end of the selectors scope that contains the CSS3 rule causes it to render correctly in otherwise unsupported versions of IE.
Firefinder is an extension to Firebug (in Firefox) and offers the functionality to, in a quick way, find HTML elements matching chosen CSS selector(s) or XPath