Just to be sure I did everything correctly: I clicked on the link in the thread and confirmed "Open with Firefox". I was warned about installing alien software, then proceeded. After a restart, the add-on page shows Colorful Tabs 24.0. Correct?
Unfortunately, there was no effect whatsoever, everything looks as before. Should I rather try and ask the guys of the Theme Restorer add-on? As everyone else here seems to be happy with your version, maybe they have an idea what's going wrong with my setup...