userChrome.css

#main-window[tabsintitlebar="true"]:not([extradragspace="true"]) #TabsToolbar > .toolbar-items {
opacity: 0;
pointer-events: none;
}

#main-window:not([tabsintitlebar="true"]) #TabsToolbar {
visibility: collapse !important;
}
#sidebar-header {
display: none;
}

:root {
	/* Number of pixels of enlargement when URL bar is focused */
	--mbarstyler-popout-pixels: 0px; /* [0px - 7px] */
}

/*** 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 ***/