How to hide bookmarks toolbar icons in Firefox (v106, 2022) on macOS

Add:

@-moz-document url(chrome://browser/content/browser.xhtml){
    #personal-bookmarks .bookmark-item:not([container]) .toolbarbutton-icon {
        display: none !important;
    }
}

To:

/Users/<username>/Library/Application Support/Firefox/Profiles/xxxxxxxx.dev-edition-default/chrome/userChrome.css