Ho provato giusto per provare (non utilizzo mai le barre laterali) e in effetti funziona (Fx62 su Mac).
L'unico problema nel mio caso è che nella barra laterale sopra il campo "Cerca nei segnalibri" (vedi ultima immagine postata da DMD) la stella, la scritta Segnalibri e la X di chiusura sono nere su sfondo scuro e quindi non visibili in chiaro...
Questo è il codice che ho inserito nell'userChrome.css
/* Cambio colore barra laterale */
#sidebar-box, #sidebar, .sidebar-placesTree{
-moz-appearance: none !important;
color: #f9f9fa !important; /*text color*/
background-color: #1c1c1c !important; /* background color */
}
/* Modifica icona cartelle */
#bookmarks-view treechildren::-moz-tree-image(container),
#PlacesToolbarItems toolbarbutton[container="true"] .toolbarbutton-icon,
#PlacesToolbarItems menu[container="true"] .menu-iconic-left,
#BMB_bookmarksPopup menu[container="true"] .menu-iconic-icon,
#bookmarksMenu menu[container="true"] .menu-iconic-icon {
fill: #e8bb00 !important; /* slightly muted gold */
}
/* Live Bookmark (RSS Feed) */
#bookmarks-view treechildren::-moz-tree-image(container, livemark),
#PlacesToolbarItems toolbarbutton[container="true"][livemark="true"] .toolbarbutton-icon,
#PlacesToolbarItems menu[container="true"][livemark="true"] .menu-iconic-left,
#BMB_bookmarksPopup menu[container="true"][livemark="true"] .menu-iconic-icon,
#bookmarksMenu menu[container="true"][livemark="true"] .menu-iconic-icon {
fill: orange !important;
}
/* Smart bookmark folder */
#bookmarks-view treechildren::-moz-tree-image(container, query),
#PlacesToolbarItems toolbarbutton[container="true"][query="true"] .toolbarbutton-icon,
#PlacesToolbarItems menu[container="true"][query="true"] .menu-iconic-left,
#BMB_bookmarksPopup menu[container="true"][query="true"] .menu-iconic-icon,
#bookmarksMenu menu[container="true"][query="true"] .menu-iconic-icon {
fill: #69c !important; /* similar to blue smart folder color */
}
/* These "containers" are SVG in the sidebar, not yet on the menu */
#bookmarks-view treechildren::-moz-tree-image(container, OrganizerQuery_BookmarksMenu) {
fill: olive !important;
}
#bookmarks-view treechildren::-moz-tree-image(container, OrganizerQuery_BookmarksToolbar) {
fill: olive !important;
}
#bookmarks-view treechildren::-moz-tree-image(container, OrganizerQuery_UnfiledBookmarks) {
fill: olive !important;
}
/* Avoid overriding classic Bookmarks Toolbar and Other Bookmarks icons in menus */
#BMB_bookmarksPopup #BMB_bookmarksToolbar.menu-iconic-icon,
#bookmarksMenu #bookmarksToolbarFolderMenu.menu-iconic-icon {
list-style-image: url("chrome://browser/skin/places/bookmarksToolbar.png") !important;
}
#BMB_bookmarksPopup #BMB_unsortedBookmarks.menu-iconic-icon,
#bookmarksMenu #menu_unsortedBookmarks.menu-iconic-icon {
list-style-image: url("chrome://browser/skin/places/unsortedBookmarks.png") !important;
}