The Alpha 3 release includes support for animated PNG (define) graphics, which would mark the first new browser to include a default animated file format in more than a decade. Animated GIFs and JPEGs were a common development in the early days of the Web. The PNG format is considered to be more scalable than either GIF or JPEG and does not have the same patent issues that surround the use of GIF.
Firefox 3 Alpha 3 also adds a number of new security-related enhancements to the browser. Support for a cookie attribute called "HttpOnly" will make a cookie only readable as a server and not client-side scripts. The attribute could well serve to limit the potential exposure of personally identifiable information to unauthorized scripts that are running on a user's PC.
Since the days of Marc Andreessen's first Netscape release, browsers have included a history cache, which enables users to go back to recently viewed content. In the modern world of AJAX-infused Web sites, that caching feature has fallen somewhat short.
Firefox 3.0 Alpha 3 is taking steps to help fix the off-line problem with support for the new off-line resource tag, which will ensure browser resources are available for cached content even when the browser is not connected to the live online resource.