"Leaked firmware" refers to computer software that was not intended to be made public but somehow got released or shared without authorization. Full definition
The version in the current leaked firmware remains a little buggy. (androidcentral.com)
In order to successfully manage to install this new Android 4.2.2 Jelly Bean leaked firmware for your Samsung Galaxy S3, then you first take a look at the preparation guide below: (android.gs)
This info comes from XDA Developers and FunkyHuawei, and is based on leaked firmware files. (androidheadlines.com)