@namespace url(http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul);

tab.tabbrowser-tab:nth-child(1) { background-color: #CCCCDD !important; }
tab.tabbrowser-tab:nth-child(2) { background-color: #CCDDCC !important; }
tab.tabbrowser-tab:nth-child(3) { background-color: #CCDDDD !important; }
tab.tabbrowser-tab:nth-child(4) { background-color: #DDCCCC !important; }
tab.tabbrowser-tab:nth-child(5) { background-color: #DDCCDD !important; }
tab.tabbrowser-tab:nth-child(6) { background-color: #DDDDCC !important; }
tab.tabbrowser-tab:nth-child(7) { background-color: #DDDDDD !important; }
tab.tabbrowser-tab:nth-child(8) { background-color: #BBBBBB !important; }