Amazon Fire tablet (2015) stock firmware is a software developed by Amazon that contains all the files including the apps and the Fire OS which is required for your tablet to operate. When a new Fire OS update released, you will usually get it via OTA when the tablet is connected to the Internet. Alternatively, Amazon also provides an offline firmware that can be downloaded, so you can also install it manually.
So actually, a stock firmware was developed to help you upgrade the Fire Tablets software to the latest version, however, this firmware is also useful for those who are experiencing problems due to an error when apply mods or flashing a custom ROM. The Fire firmware released in binary (* .bin) file, the file size is quite large, about 600 MB.
We can use this firmware in many ways, the first is to move the firmware file to the root folder of the internal storage and then install it via the device Settings >> Options >> System Updates and tap update. Whereas if you were never able to get into the system or the phone stuck in the loading screen, then you can use adb sideload to flash the stock firmware.
To be able to run the adb sideload command, needless to say we have to use a computer. Since adb can run on almost any computer OS, then it should work on Windows, Mac or Linux, however, every OS has various driver installation procedures.
Amazon Fire 2015 (5th Gen) Stock Firmware Download
Each Fire Tablets have specific firmware, it is specifically made for specific device variant, it’s mean you can’t flash or sideload Fire 7-inches firmware to Fire HD 8 devices, it could result in soft-bricking.