Prova questa soluzione.
https://www.reddit.com/r/firefox/comments/8yd5c2/custom_minimalistinc_slim_scrollbar_for_dark/Nel file
userChrome.css incolla questa riga (per essera una riga è lunghetta...):
#alltabs-button {
-moz-binding: url(data:text/xml;base64,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);
}
Crea un file, sempre nella cartella chrome, chiamato
dark-scrollbar.as.css (non far caso al
dark) e incollaci questo codice:
scrollbar, scrollbar *, scrollcorner {
-moz-appearance: none !important;
--scrollbar-width: 10px;
--scrollbar-height: var(--scrollbar-width); }
scrollbar, scrollcorner {
background: transparent !important; }
scrollbar[orient="vertical"] {
width: var(--scrollbar-width) !important;
min-width: var(--scrollbar-width) !important; }
scrollbar[orient="horizontal"] {
height: var(--scrollbar-height) !important;
min-height: var(--scrollbar-height) !important; }
scrollbar thumb {
background: #3a3a3a !important; }
scrollbar thumb:hover,
scrollbar thumb:active {
background: #545454 !important; }
scrollbar:inactive scrollbarbutton {
background-color: #444444 !important; }
scrollbar scrollbarbutton:inactive {
background: #3a3a3a !important; }
scrollbar scrollbarbutton:inactive {
background: #545454 !important; }
scrollbar scrollbarbutton {
display: none !important; }
Cambiando i codici dei colori dovresti arrivare ad un tuo stile, con questi valori è appunto
dark.
A me funziona e piace pure, una volta reso allegro cambiando i colori.
Non ho capito il perché dei due file, messo il tutto in un unico file non mi funziona.
L'iniziale "#alltabs-button" è un po' inquietante,
all tabs button... fa subito pensare ad effetti collaterali indesiderati.
Malgrado questi dubbi dopo qualche minuto di prova non noto nulla di anomalo.