My UserChrome Setup (Dec20)

/* 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: #e8bb00 !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: orange !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;
}





/* transucent tabs https://www.reddit.com/r/FirefoxCSS/comments/gqc8ox/enabling_transparency_in_macos_catalina_10154/
from user https://www.reddit.com/user/TheEpicRedCape/*/
:root #TabsToolbar {

-moz-appearance: -moz-mac-vibrant-titlebar-dark !important;

-moz-font-smoothing-background-color: -moz-mac-vibrant-titlebar-dark !important;

}

/* mac-vibrant-titlebar https://www.reddit.com/r/FirefoxCSS/comments/gqc8ox/enabling_transparency_in_macos_catalina_10154/*/

:root {
  background: transparent !important;
}

#main-window {
  background: transparent !important;
}

#TabsToolbar, .table-widget-empty-text {
  -moz-appearance: -moz-mac-vibrant-titlebar-dark !important;
  -moz-font-smoothing-background-color: -moz-mac-vibrant-titlebar-dark !important;
}

#TabsToolbar,.tab-background-inner,.theme-dark,.theme-light,slider,.CodeMirror,.devtools-toolbar,.message,.theme-body,.table-widget-empty-text {
  -moz-appearance: -moz-mac-vibrancy-dark !important;
}

.theme-body {
  background: transparent !important;
}

.tab-background:not([selected="true"]) {
  -moz-appearance: -moz-mac-vibrancy-dark !important;
}

/* mac-vibrant-titlebar-fix */

#navigator-toolbox {
  margin-bottom: -1px !important;
}

/* /mac-vibrant-titlebar-fix */