The preview doesn't even work in Firefox, which is disappointing.

I love the idea, however, the format doesn't work for me at all. Showing the startup's website takes a long time to load, and it's a bad user experience.

Instead what you want to show people who open a new tab is a standardized UI (I'd go for: the startup name, what is does in one line, one standard-sized image, some text, and a link). If you'd do that, you could preload one or several startups and make those tabs load instantly. That way it's a lot less jarring and distracting for the user.

Also, a Firefox version is a must-have.