itch.io

I'll just cite myself:

I'm afraid it's not a glitch. It's a performance issue that can vary from user to user. Some PCs can be laggy when it comes to browser games. When you play a downloadable mod it runs using your PC's GPU — no inputs lags, great performance, etc. Browsers, however, do not always use the GPU relying on the CPU only. FNF is a CPU-heavy game so I'd recommend two things: 1) enable hardware acceleration in your browser's settings; 2) if you are on a Windows laptop, go to the Graphics Settings and make the OS run your browser using the laptop's discrete GPU (if it has one) to help the CPU calculate stuff.