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At first, I don't know why to use a 3D web browser, the browser must be very simple contrary to 3D browsers (as I think), SphereXPlorer and uBrowser are three-dimensionals browsers.
uBrowser is a free and open-source (Download the source code or the executable) and there are several screenshots, for more information and resources visit www.ubrowser.com.
For SphereXPlorer browser, you can download it from here : SphereXPlorer v0.55 and there are several screenshots too.

The SphereXPlorer is a three-dimensionals web browser. Enables you to browse the web like you had never before. The interface is based on experience and technology gained from the SphereXP project.

uBrowser is a simple Web Browser that illustrates one way of embedding the Mozilla® Gecko rendering engine into a standalone application using LibXUL. In this case, the contents of the page is grabbed as it's being rendered and displayed as a texture on some geometry using OpenGL™. You are able to interact with the page (mostly) normally and visit (almost) any site that works correctly with Firefox® 1.5.

Its purpose is to provide a test bed and a proof of concept for the software I'm working on at Linden Lab. By releasing the source code I'm hoping that others can benefit from what I've learnt as well as help fix bugs and identify areas for improvement. It is not meant as a replacement for your regular 2D browser.