A beta version of the fifth version of the Firefox web browser for downloading and testing has been released by Mozilla. He mentioned in his blog that this release includes the Firefox channel switcher, performance and stability enhancements and support for the new CSS animations standard. The new Firefox channel switcher makes users test features at various levels of development, quality and polish, meanwhile, the Firefox Aurora development channel to support more frequent releases.

Source: http://www.computerweekly.com/Articles/2011/05/23/246756

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