Apple today issued build 12E30 of OS X Mountain Lion to developers, eight days after the first beta of OS X 10.8.4 was released. The first build asked developers to focus on Wi-Fi, Graphics Drivers and Safari, with no issues mentioned.
Registered developers can download the update on Apple's Developer Page
Top Rated Comments
I find it strange that although the release notes clearly tells developers to focus on Safari, it still has the same build as 10.8.3; Version 6.0.3 (8536.28.10).
Probably updated Webkit rather than the actual app.