Warning, /plasma/breeze-gtk/src/gtk3/applications/_firefox.scss is written in an unsupported language. File is not indexed.

 #MozillaGtkWidget {
         scrollbar {
                 padding: 0px;
                 slider {
                         margin: 0px;
                         background: none;
                         background-color: gtkalpha(gtk("@theme_fg_color"), 0.5);
 
                         &:hover {
                                 background-color: gtkalpha( gtk("@theme_button_decoration_hover"), 0.5);
                         }
                         &:focus {
                                 background-color: gtkalpha( gtk("@theme_button_decoration_focus"), 0.5);
                         }
                 }
         }
 }