Sorry I'm a little late posting this... didn't see it until now. 
Anyway... 4.0b5 (and 3.6.9) both add support for a header called X-FRAME-OPTIONS that can be used to block or limit frame usage - its primary purpose is to stop cross-site scripting (XSS) attacks.
Additionally, support for the provisional HTML5 audio manipulation standard has been added. This permits JavaScript to interface with audio and video elements.
Get it here: http://www.mozilla.com/en-US/firefox/all-beta.html
Anyway... 4.0b5 (and 3.6.9) both add support for a header called X-FRAME-OPTIONS that can be used to block or limit frame usage - its primary purpose is to stop cross-site scripting (XSS) attacks.
Additionally, support for the provisional HTML5 audio manipulation standard has been added. This permits JavaScript to interface with audio and video elements.
Get it here: http://www.mozilla.com/en-US/firefox/all-beta.html