
Samsung GALAXY 2013
The latest firmware for Samsung GALAXY 2013 (GT-B9120) is B9120ZNLH1 with Android 2.3.6 (Gingerbread), released on August 4, 2012 for 1 region (CSC). Every official firmware build for GT-B9120, newest first: one row per build with all regions (CSC) that received it.
Each firmware build has its own page at https://samfirm.shop/build/{PDA}, where {PDA} is the build number from the list above. Example: https://samfirm.shop/build/B9120ZNLH1

GT-B9062

GT-B5512B

GT-B5512

GT-B5510L

GT-B5510

GT-B9388

GT-B9150

GT-B5330L
You can find the firmware on the model: GT-B9120 page.
Yes, all firmware files for GT-B9120 are 100% official, original, and obtained directly from Samsung servers.
To flash GT-B9120, you need to download the appropriate firmware, put your device into Download Mode, and use the Odin tool to load the BL, AP, CP, and CSC files.
Downgrading is only possible if the bootloader version (binary bit) of the old firmware matches the current one. Always check the binary version before flashing GT-B9120.