The use of backdrop-filter triggers a fascinating bug in Firefox if you have manually enabled it (about:config, layout.css.backdrop-filter.enabled = true): the menus have a `backdrop-filter: blur(25px)`, and when they’re closed, the menus are hidden with `visibility: hidden` (I can’t see any reason why `display: none` is not used, you should normally prefer it), and this triggers https://bugzilla.mozilla.org/show_bug.cgi?id=1600485, where the blurred backdrop still gets rendered, making the areas underneath those menus basically useless as they’re blurred beyond recognition.
Without having opened the page: visibility can be animated using CSS transitions, so you can fade in/out the menus. Display doesn't work that way, so that's probably the reason.
