The version I9300XXUFME7 seems to be the latest firmware that SamMobile got their hands onto and according to their tests features that were present only in Galaxy S4 up until now have been spotted in the firmware.

Testing of the Jelly Bean 4.2.2 for the Galaxy S3 is currently underway at Samsung and the official release is slated for July or August. Some of the features spotted in the leaked build are S4 like screenlock; new screen modes; Daydream; Driving mode; Actionable notifications; new additions to the notification center; revamped settings interface – exactly like the S4; addition of voice controls; gallery mode with white backgrounds; full screen Samsung apps; new s-Voice; and smart switch widget.

You can head onto SamMobile to download the test build checkout instructions on how to install the test build on your S3.