Potresti provare se il solo codice css del file che attivi, messo nel tuo userChrome.css funziona. In altri termini, provare se funziona da solo oppure se necessita di altro codice presente in altri file di questa collezione.
Per comodità riporto qui il codice:
:root {
--tabs_toolbar_color_tabs_not_on_top: linear-gradient(#f9f9fa,#f9f9fa);
--tab-min-height_tnot: 32px;
--tab_below_navigation_toolbar_bottom_padding: calc( var(--tab-min-height_tnot) + 5px );
}
#TabsToolbar {
position: absolute;
display: block;
bottom: 0;
width: 100vw;
background-clip: padding-box;
color: var(--toolbar-color);
z-index: 2;
}
#TabsToolbar:not(:-moz-lwtheme){
appearance: none;
background-image: var(--tabs_toolbar_color_tabs_not_on_top) !important;
}
#main-window:not([tabsintitlebar]) #TabsToolbar:not(:-moz-lwtheme){
appearance: none !important;
}
#tabbrowser-tabs {
width: 100vw;
}
#navigator-toolbox {
position: relative;
padding-bottom: var(--tab_below_navigation_toolbar_bottom_padding);
}
#main-window[tabsintitlebar]:not([inDOMFullscreen="true"]) #titlebar,
#main-window[tabsintitlebar][sizemode="maximized"]:not([inDOMFullscreen="true"]) #titlebar {
height: 26px;
}
/* prevent possible item overlapping with caption buttons */
#main-window[tabsintitlebar] #toolbar-menubar {
padding-inline-end: 140px;
}
/* move caption buttons to windows top right position */
.titlebar-buttonbox-container {
position: fixed;
right: 0;
visibility: visible;
display: block;
}
#TabsToolbar .titlebar-buttonbox-container,
#TabsToolbar .private-browsing-indicator,
#TabsToolbar #window-controls,
#TabsToolbar *[type="caption-buttons"],
#TabsToolbar *[type="pre-tabs"],
#TabsToolbar *[type="post-tabs"] {
display: none;
}
/* lw themes support */
#nav-bar {
box-shadow: unset !important;
}
/* remove color overlay for lw-themes */
#main-window[style*='--lwt-header-image'] :is(#nav-bar,#PersonalToolbar,#TabsToolbar):-moz-lwtheme{
background: unset !important;
}
/* adjust background color */
#main-window:not([style*='--lwt-header-image']) #TabsToolbar:-moz-lwtheme {
appearance: none !important;
background-image: linear-gradient(var(--toolbar-bgcolor),var(--toolbar-bgcolor)) !important;
}
/* Fixes for projects other settings */
/* remove application/hamburger button in titlebar and tab toolbars start padding */
#main-window[tabsintitlebar][sizemode="fullscreen"] #navigator-toolbox #PanelUI-button {
visibility: collapse;
}
/* override code inside appbutton in titlebar code */
#main-window[tabsintitlebar] #toolbar-menubar[autohide="true"][inactive="true"] ~ #TabsToolbar,
#main-window[tabsintitlebar][sizemode="maximized"] #toolbar-menubar[autohide="true"][inactive="true"] ~ #TabsToolbar,
#main-window[tabsintitlebar][sizemode="fullscreen"] #TabsToolbar,
#main-window[uidensity=compact][tabsintitlebar] #toolbar-menubar[autohide="true"][inactive="true"] ~ #TabsToolbar,
#main-window[uidensity=compact][tabsintitlebar][sizemode="maximized"] #toolbar-menubar[autohide="true"][inactive="true"] ~ #TabsToolbar,
#main-window[tabsintitlebar]:is([sizemode="normal"],[sizemode="maximized"],[sizemode="fullscreen"]) #navigator-toolbox #TabsToolbar {
padding-inline-start: 0px !important;
margin-inline-start: 0px !important;
}
/* remove restored border between navigation toolbar and tabs toolbar */
#nav-bar:not(:-moz-lwtheme) {
box-shadow: unset !important;
}