Click download

This is a quick look on the latest leaked Android 4.2.1 JB for the galaxy S3
You can download and flash this firmware like any firmware by Odin
Generally this update is a good step for the galaxy S3, i hope Samsung will improve the official update

Whats new in jelly bean 4.2.1 update :
1- New Lock screen and widgets
2- Notification drawer : New tab for all the quick settings icons
4- MyFiles : the files saved to emulated/0 (internal storage)
5- Gallery : The title bar when viewing pictures became transparent
6- Settings :
- "My Sound" has been added to "Sounds" settings
- "Driving Mode" has been added to "Language and Input" settings
- (New) "Access to my location" and "My Places" have been added to "Location Services" settings
- "Cloud" has been returned to "Settings"
- "Voice Command" has been returned to "Settings"
- (New) "Daydream" has been added to "Display" settings
- (New) "Smart Pause" and "Smart Scroll" have been added to "Smart screen" settings (not working)
- Activating "Developer options" from "About device" by tapping 4 times on "Build number"
- (New) "Verify apps" has been added to "Security" settings (Appears when installing APK files)
- "Status" has been changed to "Custom" and "Official" instead of "Modified" and "Normal"
7- There is a dark shadow at the top of the home screens in TouchWiz
anything else still the same without changes
8- Total "RAM" has been reduced to 828MB instead of 832MB
9- "Notification panel" settings has been removed
10- Scrolling Notification settings icon has been disabled
11- "Contacts" and "Phone" app still lag
12- "Lock screen" has a little lag
13- "Swipe to capture" screen animation has been disabled
Notes :
~ This firmware isnt official mean if you flashed it , your device binary counter will be increased and status will be changed to "Modified"

Downloads :
i9300 - XXUFMB3 firmware http://goo.gl/3LB4K

Google™ has been updated the Google Play™ store to version 4.0.25 for all Android devices