Firefox 3 has carried out several improvements in support of CSS. Such upgrades are enumerated on the official documentation but this article will provide a quick tour for developers who are looking for these improvements.

 Firstly, Firefox 3 now implements the display property’s inline-block and inline-table values.
 All platforms can now support the font-size-adjust property, which previously only worked on Windows.
 rgba() and hsla() support for color (bug 147017) have been introduced
 :default pseudo-class support (bug 302186)
 -moz-max-content, -moz-min-content, -moz-fit-content, and -moz-available values have been added to width, min-width, and max-width (bug 311415 and bug 402706)
 The browser now supports HTML soft hyphens (­).
 Pre-formatted tabs, which work better in proportional fonts, now follow the CSS 2.1 spec.
 Support for ime-mode property.
 Support for the CSS text-rendering property for HTML
 -moz-border-*-start and -moz-border-*-end CSS properties have been implemented (bug 74880)
 -moz-initial is now supported for almost all CSS properties (except quotes and -moz-border-*-colors) bug 80887.
 window.getComputedStyle() now supports all CSS properties (bug 316981).
 content’s none value is now supported (bug 378535)
 cursor’s none value is now supported (bug 346690)
 The proper clipping of background images to a -moz-border-radius (bug 24998) has been enabled
 Support for white-space’s pre-wrap value (bug 261081)
 Selectors like :first-child, :only-child, :last-child (bug 73586), :empty (bug 98997), or the + combinator (bug 229915) have been dynamically updated (bug 401291).
 Negative z-index values are now aptly supported

Firefox 3 introduced changes on the Document Object Model (DOM) as well. Support for extensions to the DOM added by other browsers was especially improved. Here’s a short enumeration of these additional upgrades:
 Support for the Internet Explorer clientTop and clientLeft DOM extensions
 Improved accuracy for the window.fullScreen property regardless of where it is being read, including in content. It used to return false inaccurately (bug 127013)
 Support for the getClientRects and getBoundingClientRect DOM extensions (see bug 174397)
 Support for the Internet Explorer elementFromPoint DOM extension (bug 199692)
 Support for the Internet Explorer oncut, oncopy, and onpaste DOM extensions (bug 280959)
 privileged-code-only getters for Node.nodePrincipal, Node.baseURIObject, and document.documentURIObject have been added. Chrome code must neither get or set these properties on an unwrapped content object (ie. on a wrappedJSObject of an XPCNativeWrapper), refer to bug 324464
 Support for the Web Applications 1.0 (HTML5) getElementsByClassName() DOM method
 Support for the Web Applications 1.0 (HTML5) window.postMessage DOM. This system enables a limited, opt-in form of client-side communication between windows but not necessarily on a common domain.
 The charCode value of the keypress event is converted into an ASCII character if the accelerator key is pressed. Otherwise the charCode is the unmodified character except when in Shift state. (Refer to Gecko Keypress Event for details)

Tags: CSS Upgrades under Firefox 3