[DecoySalamander]

There is a Tree Style Tab addon for Firefox, but it's nowhere near as polished as what's shown in the promo video. There's nothing like this in Chrome, since Chrome doesn't offer access to any browser UI elements beyond a popup over the extension's icon in the navbar. At one point I even tried to do my version of a vertical/hierarchical tab sidebar that would live in an extra tab in the Dev Tools drawer, but had to give up when I realized that there's no way to keep Dev Tools automatically open on every page.

I think it's a cool idea and something I'd buy for 20-60$, but only if it was an addon, not its own standalone browser. Those are too important to get from a tiny startup.