Earlier November Apple has seeded Safari 5.1.2 Beta for the developers in order to get bug fixes and test improvements and just now Apple has released the final Safari 5.1.2 version. The new Safari update brings PDF support for webpages which allows the users to view PDF documents right inside Safari browser rather than opening in separately in third party applications. In addition to new features one of the major bug reported in last build was white screen while browsing that has also been fixed apart from other performance and memory fixes.
To get the update you can head over to update center on your Mac or download it directly from here.