userChrome.css

/* Hide all tab Close buttons */
.tabbrowser-tab .tab-close-button{display:none!important}

/* Disable "Pin to Overflow Menu" and "Remove from Toolbar" context menu entries */
.customize-context-moveToPanel,.customize-context-removeFromToolbar{color:GrayText;pointer-events:none}

/*** Revert tab throbber - for Firefox 80 as of 8/28/2020 ***/
.tab-throbber[busy] {
  background-image: url("chrome://global/skin/icons/loading.png") !important;
  animation: unset !important;
}
.tab-throbber[busy]:not([progress]) {
  /* Grays the blue during "Connecting" state */
  filter: grayscale(100%);
}
@media (min-resolution: 2dppx) {
  .tab-throbber[busy] {
    background-image: url("chrome://global/skin/icons/[email protected]") !important;
  }
}
/* Suppress bouncing dots when ui.prefersReducedMotion = 0 */
.tab-throbber[busy]::before {
  background-image: none !important;
  animation: unset !important;
}
@media (min-resolution: 2dppx) {
  .tab-throbber[busy]::before {
    background-image: none !important;
  }
}

/*** BEGIN Firefox 77 (June 2, 2020) Override URL bar enlargement ***/

/* Compute new position, width, and padding */
#urlbar[breakout][breakout-extend] {
    top: 5px !important;
    left: 0px !important;
    width: 100% !important;
    padding: 0px !important;
}

/* for alternate Density settings */
[uidensity="compact"] #urlbar[breakout][breakout-extend] {
    top: 3px !important;
}
[uidensity="touch"] #urlbar[breakout][breakout-extend] {
    top: 4px !important;
}

/* Prevent shift of URL bar contents */
#urlbar[breakout][breakout-extend] > #urlbar-input-container {
    height: var(--urlbar-height) !important;
    padding: 0 !important;
}

/* Do not animate */
#urlbar[breakout][breakout-extend] > #urlbar-background {
    animation: none !important;;
}

/* Remove shadows */
#urlbar[breakout][breakout-extend] > #urlbar-background {
    box-shadow: none !important;
}

/*** END Firefox 77 (June 2, 2020) Override URL bar enlargement ***/