Google’s Android is the most popular mobile operating system followed by Apple’s iOS and Microsoft’s Windows Phone. While the other two OSs are closed in nature, Android is open source and allows after-market development activities through rooting and customized recovery.

However, besides the above-listed rulers of the smartphone industry, there are a number of other operating systems, good and bad, that are still struggling to win the attention of users. The first previews of the Ubuntu OS for mobile devices looked really charming. It was ported to several Android devices in the partly functional state. However, the curiosity phase of Ubuntu OS soon faded out and now we have another ambitious project from the Mozilla family that is having a difficult time in creating a space for itself in the market.

Mozilla’s Firefox OS might be struggling to compete with the bigger giants but, like Ubuntu OS, it has finally made its way into Android. XDA member abtekk has been releasing his ported Firefox OS for the Nexus 5 because April, but all the earlier versions of his port had major bugs. Finally, he has uploaded the most recent nightly of the OS that can be said to be highly (if not fully) functional.

If you are an adventurous Nexus 5 user who is keen to give a try to the Firefox OS, it’s your time to experience something new. the most recent nightly of ROM is available as system images that can be flashed using Fastboot command just like you install the factory images. The performance of the ROM is a little laggy and you might experience occasional glitches while scrolling the screen. The only major feature that did not work for me was the camera. everything else, including phone, data, and WiFi work fine.

Screenshots:

Warning
The procedure described below is not implied for noobs, so stay away if you do not understand what it really is. During Firefox OS  installation on your Nexus 5 all the SD card data, apps, root access, customized recovery present on your Nexus 5 will be wipe. Therefore, we strongly recommend you to backup everything. The only way to return your phone back to stock Android is by flashing the Nexus 5 factory images.

Prerequisites
Before you can get the Firefox OS working on your Nexus 5, below are some preparations to be made:

Download the most recent Firefox OS nightly: ffos_abtekk-hammerhead.zip

Setup ADB and Fastboot on your computer. If you do not how to do so, read our tutorial.

Enable Android Debugging on your Nexus 5 from Settings> developer options. To activate developer options, read these instructions.

Make sure you have installed Google USB chauffeurs on your computer.

Charge your phone to guarantee 60% battery level.

Backup all essential data and apps before proceeding.

Installing Firefox OS on Nexus 5

Extract the ffos_abtekk-hammerhead.zip file to get the flashable images. You will see four files inside the extracted folder:

boot.img

cache.img

system.img

userdata.img

Copy these files to the platform-tools or ADB-Fastboot folder.

Now launch a command prompt from inside the folder where you have copied the .img files.

Connect your Nexus 5 to the computer and issue the following command and hit enter essential to reboot the device into Bootloader/Fastboot mode:
adb reboot bootloader

When the phone shows up the Bootloader screen with start written on the top, flash the images one by one using the following commands:
fastboot flash system system.img
fastboot flash boot boot.img
fastboot flash userdata userdata.img
fastboot flash cache cache.img

When all images are flashed, run the following command:
fastboot reboot-bootloader

Finally, reboot the device.

When your Nexus 5 boots up, you’ll see Firefox OS setup. just go through the setup and you will be welcomed by the home screen. Enjoy Firefox OS on your Nexus 5! In case you want to return to stock Android, use the following guide:

Restore Nexus 5 to stock and Flash factory Images

Also See: Nexus 5 suggestions and Tricks