After the release of mozilla Firefox 4 beta 11, Mozilla release its another updated version of firefox where many small and bug fixed already. In this version of FireFox many features are upgrade as you know that performance and speed is a big issue before, but now it comes with more responsiveness when you are watching videos on internet. And company is already fixed more than 7,000 bugs after the first beta.
you can download Mozilla FireFox 4 Beta 12 from given links below or you can download it directly from your current firefox automatic update.
Download Mozilla FireFox 4 Beta 12 for windows
Download Mozilla FireFox 4 Beta 12 for Mac OS X