userChrome.css

#TabsToolbar {
  visibility: collapse;
}

/* Remove title section from Tree Style Tabs */
/* #sidebar-box[sidebarcommand="treestyletab_piro_sakura_ne_jp-sidebar-action"] > #sidebar-header { */
/*      visibility: collapse;   */
/* } */

/* Compact tab layout */
:root { --tab-height: 20px !important; }
.tab { height: 20px !important; }
/* Shrink space between pinned tabs and tab bar, only when pins are present */
#tabbar[style*="margin"] { margin-top: 20px !important; }

/* Show title of unread tabs with red font */
.tab.unread .label {
  color: red !important;
}

/* Add private browsing indicator per tab */
.tab.private-browsing .label:before {
  content: " ";
}

#navigator-toolbox[fullscreenShouldAnimate] {
    transition: none !important; 
}

:root {
  --sidebar-min-width: 40px;
  --sidebar-visible-width: 300px;
  --margin-offset: -5px;
}

#sidebar-header {
  overflow: hidden !important;
}

#tabbrowser-tabs {
  visibility: collapse !important;
}

#sidebar-box #sidebar-header {
    display: none !important;
}

#sidebar,
#sidebar-header {
  position: relative !important;
  min-width: var(--sidebar-min-width) !important;
  max-width: var(--sidebar-min-width) !important;
  transition: .1s ease .15s;
  z-index:1;
}

/* Margin when collapsed */
#sidebar-box :-moz-any(#sidebar,#sidebar-header) {
    margin-right: var(--margin-offset) !important;
}

#sidebar-box:hover :-moz-any(#sidebar,#sidebar-header) {
  background-color: var(--toolbar-bgcolor) !important;
  min-width: var(--sidebar-visible-width) !important;
  max-width: var(--sidebar-visible-width) !important;
  margin-right: calc((var(--sidebar-visible-width) - var(--sidebar-min-width) - var(--margin-offset)) * -1) !important; /* To keep the page occupying the same size */
  z-index:1;
  position: relative !important;
  transition: .1s ease .15s;
}

#TabsToolbar > .toolbar-items,
#TabsToolbar > .titlebar-spacer{ visibility: hidden }
/* #nav-bar{ margin-top: -32px; margin-right: 20px; padding: 0px 150px 0px 0px !important; } */

/* Dark scrollbar */

:root{
  scrollbar-face-color: rgb(210,210,210); /* Firefox 63 compatibility */
  scrollbar-track-color: rgb(46,54,69); /* Firefox 63 compatibility */
  scrollbar-color: rgba(0,0,0,.4) rgba(140,140,140,0.1);
  scrollbar-width: thin;
}