You can make it look better by giving FF a dark theme. I agree it doesn't look great out of the box. As for the use case, I don't think it's an understatement

You can make it look better by giving FF a dark theme. I agree it doesn't look great out of the box. As for the use case, I don't think it's an understatement to say it changed how I browse the web. Before I discovered Tree Style Tabs, I was like you -- I only kept a few tabs open and was diligent about maintaining a coherent working set. Now, I build hierarchical structures of nested tabs based on what I'm working on, and I easily reach the 60+ tab range on a daily basis. Instead of those tabs feeling like a burden, it's trivial to make use of all of them without feeling like anything is cluttered. I can maintain so much more organized information at my finger tips in Firefox than I ever could before.