Firefox 3.6 alpha releases have already arrived and there are already cool new features on the heals of the 3.5 release, as well as rapid speed improvements.

People have focused on the new CSS improvements (Acid3 now gets 94/100) such as the tweaked CSS gradient support:

We also get new background rules such as background-size and multiple backgrounds.

Read more 3.6 for developers info:

• The background-size property from the CSS 3 Backgrounds and Borders draft is supported under the name -moz-background-size .
• A proposal for CSS gradients is supported for background-image .
• Multiple background images are now supported.
• The rem length unit from CSS3 Values and Units is now supported.
• image-rendering is supported for images, background images, videos and canvases.
• text-align :end is now supported
• DOM changes to elements using the table display types now work much better.

• You can determine whether or not content is being rendered on a touch-enabled device using the new :-moz-system-metric(touch-enabled) selector.

• The reorder event is now sent to embedded frames and iframes when their document is loaded. See
  bug 420845.
• The getBoxObjectFor() method has been removed, as it was non-standard and exposed even more non-standard stuff to the web. See
  bug 340571.  Also affects mootools which uses this call for Gecko detection.  See this mootools bug.
• A new attribute has been created, mozScreenPixelsPerCSSPixel, for obtaining the amount of screen pixels per CSS pixel on nsIDOMWindowUtils . This can be used in conjunction with the new global properties, mozInnerScreenX and mozInnerScreenY, to compute screen coordinates. See

  bug 486200 and
  bug 507755.

• When the page’s URI’s document fragment identifier (the part after the “#” (hash) character) changes, a new hashchange event is sent to the page. See window.onhashchange for more information.
• Geolocation “address” support is now available enabling user-readable position information.  See

  bug 503942.

• The attribute document.readyState is now supported. Gecko also supports document.onreadystatechange now.
• Support for HTML 5′s element.classList to allow easier handling of the class attribute.