I run Windows 7 Ultimate, full Aero effects, and Firefox. The most recent update of Firefox to version 29.0 resulted in yet another redesign of the tabs. This redesign is very unfortunate because it makes the text completely unreadable. I have some very choice words for the Firefox developers about their general competence, but that's not what this post is about.
This post is for the average user that this garbage release was foisted upon. I've been running the fix for about a week now and, while not perfect, it is much better than not being able to read the text on my tabs at all.
Click "Add to Firefox". Done.
That's the best theme I could find that balances readability, usability, and some semblance of elegance.