These are custom compiled builds of Firefox. They have been compiled from the source released by Mozilla but with some compiler optimizations. The intent is to add some performance and speed to Firefox especially on slower systems where Firefox may tend to hang at times.
These are not the official builds and do not display the official branding. They are optimized for particular hardware and OS combination.
What if Firefox was custom built to your particular CPU and even operating system? Wouldn’t it perform faster? The answer to that is a definite yes. The following builds of Firefox are optimized for particular CPUs to run specifically for Windows. They are also optimized according to the real world uses so that it performs the best on your desktop. All builds have the full functionality as the official builds from Mozilla i.e. no loss of functionality as a result of any tweaks.
Zip Packages. Extract and use.