This page looks really bad on my system- Firefox Nightly and a UWQHD display- The black circle occupies most of the screen (obscuring the text) and it animates

This page looks really bad on my system- Firefox Nightly and a UWQHD display- The black circle occupies most of the screen (obscuring the text) and it animates very slowly. The giant black circle only shows up when the viewport is very narrow, and when it's very wide (like full-width on my screen)- if I shrink the browser window to a medium width (which is likely how it was developed), the issue goes away. Aaaaand the fact that it's not easy to automated-test things like this is why I'm mainly a back-end developer =)