I love Firefox 1.0 (PR). One of the things I tried was this tip for customizing tab colors. I wanted the active tab to look more ... active. Instead of choosing some colors manually, I used the (now deprecated) CSS 2 “system” colors in my chrome/userChrome.css file:

#browser tab {
  -moz-appearance: none !important;

#browser tab[selected="true"] {
  background-color: ActiveCaption ! important;
  color: CaptionText ! important;
  border-color: ActiveBorder ! important;

#browser tab:not([selected="true"]) { 
  background-color: InactiveCaption ! important;
  color: InactiveCaptionText ! important;
  border-color: InactiveBorder ! important;

These make the tab colors match your window colors: Active Windows/Tabs and Inactive Windows/Tabs. So now when I change my Windows color scheme, Firefox’s tabs will change color too.