Here’s a quick guide on how to install Samsung Galaxy S3 Official Firmware XXEMB5 Jellybean 4.1.2, which may also let you resolve the issues of S3 like auto restart problem, apps getting closed self etc.

Howto Install Galaxy S3 I9300 Official Firmware XXEMB5

To install S3 i9300 Official Firmware XXEMB5, please note that, you have to reinstall the OS in your device,

Disclaimer: Please note that, we are not responsible for any type of loss damage, problems or issues with your smartphone, after or in between following the given process of installing the firmware. Follow all the steps mentioned in this article carefully, else there is a chance of bricking your device for which we should not be held responsible.

Here are the steps which will help you install the firmware into your SGS3:

Note: In order to save your data like Apps, SD Card etc, you can give it a try to install this firmware without wiping out the factory reset and cache partition, but if you encounter any problem later on, you may have to follow the procedure for wiping out your data, given at the end, and then follow the steps again.

1. Make sure USB Drivers are installed for your device, else download and install Samsung Kies.
2. Also note that your battery should be 40% charged at least to start installing the new firmware.
3. Download Samsung Official Firmware XXEMB5 and also Odin, or the latest version by checking it out at Google, and extract both the files into any foler
4. Enable USB Debugging by going into
   Settings -> Applications -> Development -> USB Debugging
   or if you’re into new OS then
   Settings -> Developer options -> ( Make the Developer options top right Power button is green i.e. enabled, else press it to enable) -> USB Debugging
5. Now power off your phone properly, and then Press Volume Down + Home + Power buttons for a while, unless you see a Warning screen
6. Now press the Volume Up button to continue and you will see the Green Android guy
7. Open up Odin (preferable is to run the application to Run as Administrator, by choosing the method by right clicking on the Odin exe file)
8. Connect your phone to your computer (Windows may find and install the drivers of your device after you’re connected to the computer, so let it do so)
9. In Odin, you will see ID:COM section becomes yellow or blue, giving you signal that your device has been successfully detected by Odin
10. If not, then try to re-install the drivers of your device through Kies and/or while connecting your phone to the computer and let Windows install and detect your device in Download mode
11. Now, in Odin, click on the PDA option and choose the firmware file you have extracted, ending with tar.md5
12. Make sure Re-Partition option is unchecked
13. Click on Start button, and wait for like 4 – 5  mins to let the firmware installed successfully into your Samsung Galaxy S3
14. After successful installation, your device will be restarted automatically. You can remove the USB cable once your phone is started successfully.

Please note, if you start getting any error messages or boot loops, shut down your phone again, or pull out the battery and put it back, and enter into the Recovery mode by pressing Volume Up + Home + Power buttons for a while, and choose wipe data/factory reset and wipe cache partition, using your Volume up and Volume down buttons for navigating up and down, and choosing the options by pressing Power button. Also be noted that, this will remove the data of your phone like Apps  (may be SD card data too). Once done, follow the steps 1 – 12 again as mentioned above by installing the firmware in your phone again.