https://www.userchrome.org/what-is-userchrome-css.html#colorbookmarkfolder
を参考にして
:-moz-any(
#bookmarks-view,
#editBMPanel_folderTree,
#placesList) treechildren::-moz-tree-image(container),
#editBMPanel_folderMenuList > .menulist-label-box > .menulist-icon,
#editBMPanel_folderMenuList menupopup menuitem
を追加すればCtrl+Shift+HのフォルダもOKですね
