Website is unusable for me on Firefox as well. Nothing is clickable and "This page is slowing down Firefox. To speed up your browser, stop this page". If I block 3rd party scripts and frames in uBlock then it works better
Yeah, it happens some times when you refresh the page before the wasm audio engine is loaded - then you just need to close the window and wait for 10-15 seconds before the background processes finish and the web-site should open just fine