ctmakro
commented
6 years ago 
the profile says the piano is extremely expensive both in terms of CPU and GPU. Each frame can take hundreds of milliseconds to render. There might be resource leak or the animation is simply unoptimized for the desktop. I suggest take it off or replace it with 2d versions.
Very severe lag (when scrolling the page for example) once you click the 'Evaluate music' tab. CPU consumption goes up. The lag only affects current Chrome Tab, so I believe there's something blocking the Javascript Engine heavily. After that, even if you switch back to other tabs, the piano-caused lag persists.