Faster and more secure browsing is coming to Firefox in a big way, as the first Aurora build of Firefox 13 gets the SPDY protocol activated by default, capping off more than four months of work putting SPDY into Firefox.
Firefox 13 Aurora (download for Windows, Mac, and Linux,) doesn't include many other new features or changes that affect Firefox fans directly, but there are many under-the-hood tweaks. One is a user agent change in Firefox for Android, so that Web sites can recognize when a person is running Firefox for Android on a phone or a tablet. This means that sites that have been coded to recognize different mobile device form factors could change their appearance depending on your device.
Developer's tools also see a large batch of small improvements, such as making recently-opened but now closed panels reopen simultaneously so that tools re-appear en masse; and saving CSS files loaded locally without a save prompt for a faster workflow.