if you right-click on a table cell in Firefox then in menu appears radiation icon
https://ru.wikipedia.org/w/index.php?title=%D0%9F%D0%BE%D0%BB%D0%B8%D0%BD_%D0%B2%D0%B5%D0%B4%D0%B5%D1%82_%D1%80%D0%B0%D1%81%D1%81%D0%BB%D0%B5%D0%B4%D0%BE%D0%B2%D0%B0%D0%BD%D0%B8%D0%B5&veaction=edit