Fx 133 > Tableiste unten per CSS-Code, oder per Skript.

/* -------------------------------------------------*/
/************* aktiven Tab einfärben ****************/
/* -------------------------------------------------*/

.tab-background[selected="true"]{
    background-color:transparent !important;
    box-shadow: inset 0px 0px 40px 0px #2846fa !important;
}


/* -------------------------------------------------*/
/************* Tab ICON LAUTSÄRKE Größe ****************/
/* -------------------------------------------------*/


.tab-icon-overlay {
  fill: white !important;
  transform: scale(1.5, 1.5) !important;
}

/* -------------------------------------------------*/
/************* Mehrzeilige Lesezeichen-Symbolleiste ****************/
/* -------------------------------------------------*/


/*Mehrzeilige Lesezeichen-Symbolleiste*/

@-moz-document url-prefix("chrome://browser/content/browser.xhtml") {
     #PersonalToolbar {
        max-height: calc(25px * 3) !important;
    }
    
    #personal-bookmarks,
    #PlacesToolbar,
    #PlacesToolbar > hbox {
        display: block !important;
    }
    
    #PersonalToolbar toolbarbutton {
        min-height: 25px !important;
        max-height: 25px !important;
    }
    
    #PlacesToolbarItems {
        max-height:60px!important;
        display: flex!important;
        flex-wrap: wrap!important;
        overflow-x: visible!important;
        overflow-y: auto!important;
    }
    
    #PlacesToolbar,
    #PersonalToolbar > scrollbar {
        -moz-window-dragging: no-drag !important;
    }
    
    #PlacesToolbar #PlacesChevron {
        display: none !important;
    }

}


/* -------------------------------------------------*/
/************* Lesezeichen Sidebar - Ordner Icon gelb ****************/
/* -------------------------------------------------*/

/* Lesezeichen Sidebar - Ordner Icon gelb */

@-moz-document url("chrome://browser/content/places/bookmarksSidebar.xhtml") {
treechildren::-moz-tree-image(container) {
list-style-image: url("data:image/gif;base64,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") !important;}
}



/* -------------------------------------------------*/
/************* Lesezeichensymbolleiste - Hintergrundfarbe ****************/
/* -------------------------------------------------*/


/* Lesezeichensymbolleiste - Hintergrundfarbe */
    @-moz-document url("chrome://browser/content/bookmarks/bookmarksPanel.xhtml"), 
    url("chrome://browser/content/browser.xhtml"),
    url("chrome://browser/content/history/history-panel.xhtml"),
    url("chrome://browser/content/places/bookmarksSidebar.xhtml") {
    #bookmarks-view,sidebarheader,#sidebar-box,.sidebar-placesTreechildren,#sidebar-search-label,#sidebar-search-container,#placesList > treechildren{
    background:#000000!important;
    color:white!important;
    }
    }


/* Tableiste unten*/
#TabsToolbar {
    position: absolute;
    display: block;
    bottom: 0;
    width: 100vw;
}

#navigator-toolbox {
    position: relative;
    padding-bottom: calc( var(--tab-min-height) + 8px );
}

.titlebar-buttonbox-container {
    position: fixed;
    right: 0;
    visibility: visible;
    display: block;
}

#TabsToolbar .titlebar-buttonbox-container,
#TabsToolbar #window-controls {
    display: none;
}

#main-menubar {
    height: 28px !important;
}
          

/*...................Ab hier nur Privater Modus...................*/

/* Das lila Icon für privaten Modus oben rechts eingefügt */
#main-window[privatebrowsingmode=temporary] #PanelUI-button::before {
    margin-left: 0 !important;
    margin-right: 0 !important;
    content: '' !important;
    display: block !important;
    width: 20px !important;
    height: 30px !important;
    background: url("chrome://global/skin/icons/indicator-private-browsing.svg") !important;
    background-repeat: no-repeat !important;
    background-position: 0 8px !important;
    background-size: 25px 17px !important;
}

/* Der neue zusätzliche Eintrag: Privater Modus unter dem Tab entfernt */  
.private-browsing-indicator-with-label {
    display: none !important;
} 

.tab-background {
border-radius: 8px 8px 0px 0px !important; border-image: none !important;
}
.tab-line {
display: none;
}

.tab-close-button {
color: red !important;
}

/* Grauer Kasten: */

.browser-toolbar:not(.titlebar-color) {
  background-color: transparent !important;
}

/* Schwarze Linie */

#nav-bar:-moz-lwtheme {
  box-shadow:  none !important;
}

/*Tableiste unten*/
#TabsToolbar {
    position: absolute;
    display: block;
    bottom: 0;
    width: 100vw;
}

#navigator-toolbox {
    position: relative;
    padding-bottom: calc( var(--tab-min-height) + 8px );
}
       

/*...................Ab hier nur Privater Modus...................*/

/* Das lila Icon für privaten Modus oben rechts eingefügt */
#main-window[privatebrowsingmode=temporary] #PanelUI-button::before {
    margin-left: 0 !important;
    margin-right: 0 !important;
    content: '' !important;
    display: block !important;
    width: 20px !important;
    height: 30px !important;
    background: url("chrome://global/skin/icons/indicator-private-browsing.svg") !important;
    background-repeat: no-repeat !important;
    background-position: 0 8px !important;
    background-size: 25px 17px !important;
}

/* Der neue zusätzliche Eintrag: Privater Modus unter dem Tab entfernt */  
.private-browsing-indicator-with-label {
    display: none !important;
} 






/* Mostly transparent on dark theme */
  /* More subtle background color on selected tab */
#main-window[lwthemetextcolor="bright"] #tabbrowser-tabs:not([movingtab]) > .tabbrowser-tab > .tab-stack > .tab-background[selected=true]:-moz-lwtheme {
  background-image: linear-gradient(to right, transparent, rgba(255,255,255,0.2) 20%, rgba(255,255,255,0.2) 80%, transparent) !important;
}
  /* No top line on selected tab */
#main-window[lwthemetextcolor="bright"] .tabbrowser-tab[selected="true"] .tab-line {
  display: none !important;
}
  /* Transparent toolbars */
#main-window[lwthemetextcolor="bright"] #navigator-toolbox > toolbar:not(#toolbar-menubar):not(#TabsToolbar) {
  background-color: transparent !important;
  background-image: none !important;
}
  /* Hide tab close buttons until hovered */
.tabbrowser-tab:not([pinned="true"]):not(:hover) .tab-close-button {
  display: none !important;
}

/* Source file https://github.com/MrOtherGuy/firefox-csshacks/tree/master/chrome/tabs_on_bottom.css made available under Mozilla Public License v. 2.0
See the above repository for updates as well as full license text. */
 
/* Modify to change window drag space width */
/*
Use tabs_on_bottom_menubar_on_top_patch.css if you
have menubar permanently enabled and want it on top
*/
 
/* IMPORTANT */
/*
Get window_control_placeholder_support.css
Window controls will be all wrong without it.
Additionally on Linux, you may need to get:
linux_gtk_window_control_patch.css
*/
 
:root{ --uc-titlebar-padding: 0px; }
@media (-moz-os-version: windows-win10){
:root[sizemode="maximized"][tabsintitlebar]{ --uc-titlebar-padding: 8px }
}
#toolbar-menubar[autohide="true"] > .titlebar-buttonbox-container,
#TabsToolbar > .titlebar-buttonbox-container{
position: fixed;
display: block;
top: var(--uc-titlebar-padding,0px);
right:0;
height: 40px;
}
/* Mac specific. You should set that font-smoothing pref to true if you are on any platform where window controls are on left */
@supports -moz-bool-pref("layout.css.osx-font-smoothing.enabled"){
:root{ --uc-titlebar-padding: 0px !important }
.titlebar-buttonbox-container{ left:0; right: unset !important; }
}
 
:root[uidensity="compact"] #TabsToolbar > .titlebar-buttonbox-container{ height: 32px }
 
#toolbar-menubar[inactive] > .titlebar-buttonbox-container{ opacity: 0 }
 
#navigator-toolbox{ padding-top: var(--uc-titlebar-padding,0px) !important; }
 
.titlebar-buttonbox-container > .titlebar-buttonbox{ height: 100%; }
 

 
.titlebar-placeholder,
#TabsToolbar .titlebar-spacer{ display: none; }
/* Also hide the toolbox bottom border which isn't at bottom with this setup */
#navigator-toolbox::after{ display: none !important; }
 
@media (-moz-gtk-csd-close-button){ .titlebar-button{ flex-direction: column; } }
 
/* These exist only for compatibility with autohide-tabstoolbar.css */
toolbox#navigator-toolbox > toolbar#nav-bar.browser-toolbar{ animation: none; }
#navigator-toolbox:hover #TabsToolbar{ animation: slidein ease-out 48ms 1 }
 
/* Source file https://github.com/MrOtherGuy/firefox-csshacks/tree/master/chrome/tabs_on_bottom_menubar_on_top_patch.css made available under Mozilla Public License v. 2.0
See the above repository for updates as well as full license text. */
 
/* Menubar on top patch - use with tabs_on_bottom.css */
/* Only really useful if menubar is ALWAYS visible */
 
:root{ --uc-window-control-width: 0px !important }
 
#navigator-toolbox{ padding-top: calc(29px + var(--uc-titlebar-padding,0px)) !important }
 
#toolbar-menubar{
position: fixed;
display: flex;
top: var(--uc-titlebar-padding,0px);
height: 29px;
width: 100%;
overflow: hidden;
}
 
#toolbar-menubar > .titlebar-buttonbox-container{ height: 29px; order: 100; }
 
#toolbar-menubar > [flex]{ flex-grow: 100; }
#toolbar-menubar > spacer[flex]{
order: 99;
flex-grow: 1;
min-width: var(--uc-window-drag-space-width,20px);
}
 
#toolbar-menubar .titlebar-button{ padding: 2px 17px !important; }
 
#toolbar-menubar .toolbarbutton-1 { --toolbarbutton-inner-padding: 3px }

/* TABS: height */*|*:root { --tab-toolbar-navbar-overlap: 0px !important; --tab-min-height: 25px !important; /*adjust to set height or omit to use density*/
--tab-min-width: 80px !important; /*adjust to set width or omit to use default*/

#tabbrowser-tabs {
width: 100vw !important;
}
#main-window:not([chromehidden*="toolbar"]) #navigator-toolbox {padding-bottom: var(--tab-min-height) !important;}
 
.tab-background {
border-radius: 8px 8px 0px 0px !important; border-image: none !important;
}
.tab-line {
display: none;
}
 
.tab-close-button {
color: red!important;
}

/* Mostly transparent on dark theme */
  /* More subtle background color on selected tab */
#main-window[lwthemetextcolor="bright"] #tabbrowser-tabs:not([movingtab]) > .tabbrowser-tab > .tab-stack > .tab-background[selected=true]:-moz-lwtheme {
  background-image: linear-gradient(to right, transparent, rgba(255,255,255,0.2) 20%, rgba(255,255,255,0.2) 80%, transparent) !important;
}
  /* No top line on selected tab */
#main-window[lwthemetextcolor="bright"] .tabbrowser-tab[selected="true"] .tab-line {
  display: none !important;
}
  /* Transparent toolbars */
#main-window[lwthemetextcolor="bright"] #navigator-toolbox > toolbar:not(#toolbar-menubar):not(#TabsToolbar) {
  background-color: transparent !important;
  background-image: none !important;
}
  /* Hide tab close buttons until hovered */
.tabbrowser-tab:not([pinned="true"]):not(:hover) .tab-close-button {
  display: none !important;
}