
Samsung Galaxy S5 Active
Every official firmware build for SM-G870F0, 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/G870F0KOE1API1
Specifications of SM-G870F, a regional variant of the same device. Chipset and SIM lines are left out: they can differ by region.

SM-G870W

SM-G8750

SM-G975WC

SM-G889A

SM-G888N0
You can find the firmware on the model: SM-G870F0 page.
Yes, all firmware files for SM-G870F0 are 100% official, original, and obtained directly from Samsung servers.
To flash SM-G870F0, 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 SM-G870F0.