[moeamaya]

It's all CSS animations timed with transition-delay (but triggered with js adding a "is-active" class).

[myfonj]

FYI, there is a strange rendering glitch in current Nightly occurring while scrolling the page with menu opened: https://github.com/webcompat/web-bugs/issues/17016

If you plan to make some radical alterations that could potentially "fix" that bug in near future, could you please freeze current state somewhere until diagnosis finishes?