Opera is attacking the old “too many tabs” problem with tab stacking. The UI looks like this:

Browsers aren’t the first to encounter the problem of too many tabs.

Amazon was a famous example, it went from something like this:

To this:

Which gave way to parodies like this one:

The problem, of course, is providing access to lots of categories. In the end, they’ve moved to a different paradigm and are back to the classic left-hand navigation:

I wonder if browsers will follow a similar evolution? Perhaps not, the problem space is a little different: they don’t have to provide you access to everything in their catalogue, just to what you’ve opened. It’s more like the icons in your Windows taskbar, which have a similar problem. They solve it by letting you group items of the same type:

Interesting to see where this ends up.