It has bugs that other versions of Firefox do not. Because he does not openly share his build configuration/etc it's not possible for you to fix those bugs.
I've had to spend a lot of time trying to troubleshoot issues Pale Moon users had with my HTML5 applications, and in every case the solution was for them to use a properly built and maintained browser. :(
The answer is: No, this is my baby.
A few people have asked about getting a detailed run-down of my build
clearly not always with good intentions.
Seems more a mouthpiece for the this fellow's self-aggrandizement than anything else.
It's probably possible to produce a custom build for your machine that runs faster, whether by using custom instruction sets, or feeding different data to the optimizer when it's doing PGO. However, the risk you run there is that this could introduce bugs - Firefox and Chrome both regularly run into bugs caused by the optimizer or linker, and in some cases the fix is to stop the optimizer/linker from fiddling with that code.
No matter what tweaks I tried, the binary builds from Moz always ran better.
That being said, things like choosing the wrong preemption mode can introduce latency problems, etc. Most users experience higher throughput and higher latency when comparing Windows to Gentoo. I believe the higher user interface latency is the general case when going from Windows to Linux.