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;
}
:root { --thin-tab-width: 10px; }
:root { --wide-tab-width: 350px; }


/* Hide splitter, when using Tree Style Tab. */
#sidebar-box[sidebarcommand="treestyletab_piro_sakura_ne_jp-sidebar-action"] + #sidebar-splitter {
  display: none !important;
}
/* Hide sidebar header, when using Tree Style Tab. */
#sidebar-box[sidebarcommand="treestyletab_piro_sakura_ne_jp-sidebar-action"] #sidebar-header {
  visibility: collapse;
}

/* Shrink sidebar until hovered, when using Tree Style Tab. */
#sidebar-box:not([sidebarcommand="treestyletab_piro_sakura_ne_jp-sidebar-action"]) {
  min-width: var(--wide-tab-width) !important;
  max-width: none !important;
}
#sidebar-box[sidebarcommand="treestyletab_piro_sakura_ne_jp-sidebar-action"] {
  overflow: hidden !important;
  position: relative !important;
  transition: all 200ms !important;
  min-width: var(--thin-tab-width) !important;
  max-width: var(--thin-tab-width) !important;
  z-index: 1;
  border-right: 1px solid black !important;
}
#sidebar-box[sidebarcommand="treestyletab_piro_sakura_ne_jp-sidebar-action"]:hover,
#sidebar-box[sidebarcommand="treestyletab_piro_sakura_ne_jp-sidebar-action"] #sidebar {
  transition: all 200ms !important;
  min-width: var(--wide-tab-width) !important;
  max-width: var(--wide-tab-width) !important;
  margin-right: calc((var(--wide-tab-width) - var(--thin-tab-width)) * -1) !important;
  z-index: 1;
  border-right: 1px solid black !important;
}

/* Auto-hide bookmarks except when hovering navigator toolbox */
#PersonalToolbar{
  visibility: collapse !important;
}

#navigator-toolbox:hover > #PersonalToolbar{
  visibility: visible !important;
}


/* REMOVE MEGABAR START
 * VERSION 1.0.4
 * CODE AT: http://userchrome.wesleybranton.com/megabar
 * RELEASE NOTES: http://userchrome.wesleybranton.com/notes/megabar */
@-moz-document url(chrome://browser/content/browser.xhtml) {
    /* DISABLE EXPANDING START */
    #urlbar[breakout][breakout-extend] {
        top: calc((var(--urlbar-toolbar-height) - var(--urlbar-height)) / 2) !important;
        left: 0 !important;
        width: 100% !important;
    }

    #urlbar[breakout][breakout-extend] > #urlbar-input-container {
        height: var(--urlbar-height) !important;
        padding-block: 0 !important;
        padding-inline: 0 !important;
    }

    #urlbar[breakout][breakout-extend] > #urlbar-background {
        animation-name: none !important;
        box-shadow: 0 1px 4px rgba(0, 0, 0, .05) !important;
    }
    /* DISABLE EXPANDING END */

    /* REMOVE URL RESULT PADDING START */
    .urlbarView {
        margin-inline: 0 !important;
        width: 100% !important;
    }

    .urlbarView-row {
        padding-block: 0 !important;
    }
    /* REMOVE URL RESULT PADDING END */

    /* MOVE URL RESULT TYPE ICON TO LEFT START */
    .urlbarView-type-icon {
        min-width: 16px !important;
        height: 16px !important;
        margin-bottom: 0 !important;
        margin-inline-start: 0 !important;
    }

    .urlbarView-favicon {
        margin-inline-start: 20px !important;
    }
    /* MOVE URL RESULT TYPE ICON TO LEFT END */

    /* DISPLAY GO BUTTON WHEN TYPING START */
    #urlbar-input-container[pageproxystate="invalid"] #urlbar-go-button {
        display: block !important;
    }
    /* DISPLAY GO BUTTON WHEN TYPING END */

    /* ALWAYS SHOW PAGE ACTIONS START */
    /* DISABLED BY DEFAULT - UNCOMMENT TO ENABLE */
    /*#pageActionButton {
        display: block !important;
    }*/
    /* ALWAYS SHOW PAGE ACTIONS END */
}
/* REMOVE MEGABAR END */