I created my own theme using a background image but it seems I cannot code it right in browser.css to make the start and end curve pieces of selected tab transparent. They remain colored, I guess using the operating system's (which is Win XP) dialog color. The middle piece is fine, though, as well as the hovering. I built my theme based on https://developer.mozilla.org/en-US/docs/Building_a_Theme but customised it. Your answer would be highly appreciated! Best regards, Chaperon