Mozilla has released a new Firefox version (v60) for Android devices that brings the new Quantum CSS engine, also called Stylo. Firefox 60 for Android has brought a View Page Source option that can be accessed from the Page Action menu. This makes it easier for web developers to view the source code of a webpage. The new Firefox version also has tons of security fixes to deliver a secured web browsing experience.
You can check the availability of Firefox 60 for your Android device by visiting Google Play. Alternatively, you can download the APK file of the latest version from APK Mirror.