message: Stop overscroll in Firefox Nightly for macOS
  Firefox is working on an overscroll feature for macOS, similar to the one Safari
  has had for some time now. It doesn't really make sense in an application
  context, so this disables it.
diff: @@ -45,6 +45,8 @@ html {
  N.B. Breaks things when we have legitimate horizontal overscroll */
  height: 100%;
  overflow: hidden;
  + // Stop similar overscroll bounce in Firefox Nightly for macOS
  + overscroll-behavior: none;
  }
  body {
  