The FreakTab community is the gold standard for TV box firmware.

If you prefer to find the firmware yourself:

While stock Lollipop is stable, the Amlogic S805 is too weak for modern apps (YouTube, Kodi 19+). Consider these alternatives:

However, for most users, a clean Android 5.1.1 Lollipop flash is the right balance of stability and functionality.

The MXQ is a low-cost, unbranded Android TV box powered by the Amlogic S805 SoC (a 32-bit, quad-core Cortex-A5 CPU with Mali-450 GPU). It was popular around 2014–2016. Most MXQ S805 boxes shipped with Android 4.4.2 KitKat, but some received an unofficial or vendor-updated Android 5.1.1 Lollipop.

Key identifiers (check before downloading):