AppSecLive.org

If you can successfully reach the Internet with FoxyProxy disabled, then there's nothing wrong with your VirtualBox settings.

The WTE-style profile for Firefox on WTE includes a pre-configured Foxyproxy - I suspect that is the Foxyproxy you are using (versus installing one yourself). The WTE installed Foxyproxy has preconfigured settings for all the local proxies installed as part of WTE - WebScarab, Burp, Paros, etc. If you are wanting to use one of these local proxies, you will need to launch Firefox and that proxy like WebScarab. Then, you'll need to left-click on the little Foxyproxy icon on the status bar - bottom right. That will bring up a menu to select the pre-configured proxy setting you want - so in this example you would click "WebScarab".

If you need to setup a proxy that's not a local proxy, like if you have a proxy at work, you'll need to do one of two things:
(1) If you only need to browse through that proxy (without something like WebScarab running at the same time), you'll need to add a new configuration to Foxyproxy using the particular details of that proxy.
(2) If you need to use a local proxy like WebScarab AND the other proxy, you'll have to chain them. Basically, tell the local proxy to send its traffic "upstream" to the other proxy (like the company one). Web traffic will then work like this:
[Firefox]<===>[WebScarab]<===>[Company Proxy]<===>{Big Scary Internet}

Hopefully this helps and isn't too late to be useful.

Cheers!

Matt Tesauro - WTE project lead