userChome.css

.tab-bottom-line {
    background: var(--identity-tab-color) !important;
    opacity: 0.75 !important;
}

/* Colored folders for Bookmarks Menus, Bookmarks Sidebar, Bookmarks Toolbar, Library window, Add/Edit Bookmarks dialog
   Original: https://www.userchrome.org/samples/userChrome-color_bookmark_folders_20171219.css
   Updated for Firefox 60: https://www.userchrome.org/samples/userChrome-color_bookmark_folders_20180510.css
   Uses mods for Firefox 62 from cor-el's Sept. 15, 2018 post:
   https://support.mozilla.org/questions/1232447#answer-1151074
*/

/* Standard folder -- on Toolbar and Menus */
#PlacesToolbarItems toolbarbutton[container="true"] .toolbarbutton-icon,
:-moz-any(
#PlacesToolbarItems,
#PlacesChevronPopup,
#BMB_bookmarksPopup,
#bookmarksMenu) menu[container="true"] > .menu-iconic-left > .menu-iconic-icon,
/* Standard folder -- in Sidebar, Library, Add/Edit Bookmark dialog */
:-moz-any(
#bookmarks-view,
#editBMPanel_folderTree,
#placesList,
#placeContent) treechildren::-moz-tree-image(container),
#editBMPanel_folderMenuList > .menulist-label-box > .menulist-icon,
#editBMPanel_folderMenuList menupopup menuitem {
  fill: #cea698 !important; /* slightly muted gold */
}

/* Live Bookmark -- on Toolbar and Menus */
#PlacesToolbarItems toolbarbutton[container="true"][livemark="true"] .toolbarbutton-icon,
:-moz-any(
#PlacesToolbarItems,
#PlacesChevronPopup,
#BMB_bookmarksPopup,
#bookmarksMenu) menu[container="true"][livemark="true"] > .menu-iconic-left > .menu-iconic-icon,
/* Live Bookmark -- in Sidebar, Library, Add/Edit Bookmark dialog */
:-moz-any(
#bookmarks-view,
#editBMPanel_folderTree,
#placesList,
#placeContent) treechildren::-moz-tree-image(container, livemark) {
  fill: #cea698 !important;
}

/* Smart bookmark folder -- on Toolbar and Menus */
#PlacesToolbarItems toolbarbutton[container="true"][query="true"] .toolbarbutton-icon,
:-moz-any(
#PlacesToolbarItems,
#PlacesChevronPopup,
#BMB_bookmarksPopup,
#bookmarksMenu) menu[container="true"][query="true"] > .menu-iconic-left > .menu-iconic-icon,
/* Smart bookmark folder -- in Sidebar, Library, Add/Edit Bookmark dialog */
:-moz-any(
#bookmarks-view,
#editBMPanel_folderTree,
#placesList,
#placeContent) treechildren::-moz-tree-image(container, query) {
  fill: #69c !important; /* similar to blue smart folder color */
}

/*** Top-level "container" icons (otherwise would be Standard folder color) ***/
/* Bookmarks Menu -- in Sidebar, Library, Add/Edit Bookmark dialog */
:-moz-any(
#bookmarks-view,
#editBMPanel_folderTree,
#placesList,
#placeContent) treechildren::-moz-tree-image(container, OrganizerQuery_BookmarksMenu),
:-moz-any(
#bookmarks-view,
#editBMPanel_folderTree,
#placesList,
#placeContent) treechildren::-moz-tree-image(container, queryFolder_menu________),
#editBMPanel_bmRootItem > .menu-iconic-left,
#editBMPanel_folderMenuList[selectedIndex="1"] > .menulist-label-box > .menulist-icon {
  fill: olive !important;
}

/* Bookmarks Toolbar -- on Menus */
#BMB_bookmarksPopup #BMB_bookmarksToolbar > .menu-iconic-left > .menu-iconic-icon,
#bookmarksMenuPopup #bookmarksToolbarFolderMenu  > .menu-iconic-left > .menu-iconic-icon,
/* Bookmarks Toolbar -- in Sidebar, Library, Add/Edit Bookmark dialog */
:-moz-any(
#bookmarks-view,
#editBMPanel_folderTree,
#placesList,
#placeContent) treechildren::-moz-tree-image(container, OrganizerQuery_BookmarksToolbar),
:-moz-any(
#bookmarks-view,
#editBMPanel_folderTree,
#placesList,
#placeContent) treechildren::-moz-tree-image(container, queryFolder_toolbar_____),
#editBMPanel_toolbarFolderItem > .menu-iconic-left,
#editBMPanel_folderMenuList[selectedIndex="0"] > .menulist-label-box > .menulist-icon {
  fill: olive !important;
}

/* Other Bookmarks -- on Menus */
#BMB_bookmarksPopup #BMB_unsortedBookmarks > .menu-iconic-left > .menu-iconic-icon,
#bookmarksMenuPopup #menu_unsortedBookmarks  > .menu-iconic-left > .menu-iconic-icon,
/* Other Bookmarks -- in Sidebar, Library, Add/Edit Bookmark dialog */
:-moz-any(
#bookmarks-view,
#editBMPanel_folderTree,
#placesList,
#placeContent) treechildren::-moz-tree-image(container, OrganizerQuery_UnfiledBookmarks),
:-moz-any(
#bookmarks-view,
#editBMPanel_folderTree,
#placesList,
#placeContent) treechildren::-moz-tree-image(container, queryFolder_unfiled_____),
#editBMPanel_unfiledRootItem > .menu-iconic-left,
#editBMPanel_folderMenuList[selectedIndex="2"] > .menulist-label-box > .menulist-icon {
  fill: olive !important;
}

/* (Older Firefox) 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;
}


/* firefox social-miedia container extenson: Making the tab underline wider and more trasaparent. https://www.reddit.com/r/FirefoxCSS/comments/8fxnb3/request_how_to_remove_tab_underline_added_by/
.tabbrowser-tab[usercontextid] .tab-bottom-line {
    display: none !important;
}
*/