Fix presentationToolbar being hidden on firefox. Fix #5354

bigbluebutton-html5/imports/ui/components/presentation/presentation-toolbar/styles.scss

@@ -18,6 +18,7 @@ $controls-background: $color-white !default;
   box-shadow: 0 0 10px -2px rgba(0, 0, 0, .25);
   align-self: center;
   justify-content: center;
+  z-index: 1;
 
   @include mq("#{$landscape} and (max-height:#{upper-bound($small-range)}), #{$small-only}") {
     transform: scale(.75);