Waterfox + Sideberry integration (v. 140+)

gistfile1.txt

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");

/* requires sidebar.revamp set to false (FF 140+) */

/* hide Sibeberry header */
#sidebar-box[sidebarcommand$="-sidebar-action"] #sidebar-header {
  display: none;
}

:root[inFullscreen] #sidebar-box[sidebarcommand$="-sidebar-action"],
:root[sizemode="fullscreen"] #sidebar-box[sidebarcommand$="-sidebar-action"], /* neither of them works */
#sidebar-box[sidebarcommand$="-sidebar-action"]:fullscreen /* like when playing video */ {
  display: none !important;
  outline: blue 1px
}

#sidebar-box {
	opacity: 0.9;
  min-width: auto !important;
}

#TabsToolbar{ visibility: collapse !important }

/* SideBerry auto-hide */

  #sidebar-box[sidebarcommand$="-sidebar-action"]:not([hidden]) {
    display: flex;
    flex-direction: column;
    overflow: hidden;
    width: 80px !important;
    /*! position: fixed; */
    z-index: 5;
    transition: all 0.12s ease !important;
    border-right: 1px solid #333; /* Adjust to fit your theme */
  }

  #sidebar-box[sidebarcommand$="-sidebar-action"]:hover {
    overflow: visible
  }
  #sidebar-box[sidebarcommand$="-sidebar-action"]:hover /*stack,*/
  #sidebar-box[sidebarcommand$="-sidebar-action"]#sidebar-header,
  #sidebar-box[sidebarcommand$="-sidebar-action"] #sidebar {
    width: 20vw !important;
  }

#sidebar-box[sidebarcommand$="-sidebar-action"] {
    height: 100vh; /* otherwise it has no heigh, and thus no size */
  }