Change the style of tab markers
From MozillaZine Knowledge Base
Some themes change the style of tab markers on the tab bar. They usually use CSS to do it, and you can add the same CSS to your user configuration files to achieve the same effect ‘permanently’, that is, irrespective of (and overriding) your chosen theme.
For example, adding the following code to userChrome.css will cause the title text of unread tabs opened in the background to appear in italics until that tab is read for the first time.
#content tab { font-style: italic !important; } #content tab[selected="true"] { font-style: normal !important; } #content tab[selected="false"] { font-style: normal !important; }