I've uploaded my current userChrome.css file (as a zip). It has tabs operating the way I like (they'll get ridiculously small and do not scroll - ever), expand properly to fill the tab area when some are closed, as you close tabs the ones to the right pull left and the "X" to close them are under your cursor, have slightly rounded (some call them square) edges, are below the URL bar, and a few other tweaks. They are "plain Jane" grey as I couldn't care less about colors on tabs. The current tab will be FF orange. An earlier post of mine has links to the site where I got my mods and has information about putting color on the tabs.