The good folks at Mozilla have announced the release of a first beta version of the next major release, v 6.0, of the Firefox browser; the beta release is available for Mac OS X, Linux, and Windows. (An Android version is also available.) The release announcement summarizes some of the new features included in this version. The Release Notes contain more technical detail, and links to further information. (The Release Notes for the Android version are here.)
Installation packages for the beta version, in a variety of (human) languages, can be downloaded here for Mac OS X, Linux, and Windows. The new version 6.0 is tentatively scheduled for final release on August 16; doing some preliminary testing now might be wise for your critical Web applications.