Hide all Firefox tab media controls

userChrome.css

/* Hide the mute/unmute button */
.tab-icon-overlay:not([sharing], [crashed]):is([soundplaying], [muted]) {
    display: none !important;
}
.tab-icon-sound {
  display: none !important;
}
.tab-audio-button { display: none !important; }
/* Keep site icon visible on hover */
.tabbrowser-tab:hover .tab-icon-stack:not([sharing], [crashed]):is([soundplaying], [muted]) > :not(.tab-icon-overlay), 
     /* for site icon with Compact density */
:root[uidensity="compact"] .tab-icon-stack:not([sharing], [crashed]):is([soundplaying], [muted]) > :not(.tab-icon-overlay) {
    opacity: 1 !important; /* overrides full transparency with full opacity */
}
/* Get rid of the green dot when media changes */
#unified-extensions-button[attention] > .toolbarbutton-icon,
.unified-extensions-item[attention] > .unified-extensions-item-action-button.toolbarbutton-1 > .toolbarbutton-badge-stack {
  background-image: none !important;
}