Safari 4.0.4 should be available through Software Update (36.2MB--requires a restart), so check there first for convenience. If you would like the standalone installer it is available for download at the Safari website: http://www.apple.com/safari/
Remember that the beta version of Firefox is a test build that has been released for development purposes. The software is not meant to be used for mainstream uses, but if you would like to check out the latest features you can install the beta along with the latest stable release. Unfortunately, as with all versions of Firefox you cannot run both versions of Firefox at the same time (which would be nice for testing purposes).
Download away, and happy browsing!