The typically vague press release mentions that the update:
- Improves stability
- Address issues that could cause hangs and excessive memory usage
- Address issues that could cause webpages to flash white
- Allows PDFs to be displayed within web content
As an aside, why hasn’t Safari found its way into the Mac App Store yet? This having to hit up both Software Update and the Mac App Store for my updates isn’t exactly optimal. One software update location to rule them all, please.