Virgin do not block any ports but the are occasional glitches so they use the proxy below when that happens.
------------------------------------------------------------------------------
Proxy for IE
------------------------------------------------------------------------------
The proxy goes in your browser.
The proxy to use is : webcache.virginmedia.com
The port number is : 8080
How to set up proxy in Internet Explorer 6/7
Step 1 � On the Tools menu in Internet Explorer, click Internet Options, click the Connections tab, and then click LAN Settings.
Step 2 � Under Proxy server, click to select the Use a proxy server for your LAN check box.
Step 3 � In the Address box, type the IP address of the proxy server. (e.g. proxy.abc.com or 202.188.17.24)
Step 4 � In the Port box, type the port number that is used by the proxy server for client connections (by default, 8080).
Step 5 � You can click to select the Bypass proxy server for local addresses check box if you do not want the proxy server computer to be used when you connect to a computer on the local network.
Step 6 � Click OK to close the LAN Settings dialog box.
Step 7 � Click OK again to close the Internet Options dialog box.
Proxy for Firefox
Here is a proxy add on for Firefox
https://addons.mozilla.org/en-US/firefox/addon/2464
To enable proxy settings in Firefox 3.0
Select Tools -> Options. ( In some Firefox browser's you have to go to Edit>Preferences usually in LInux )
Select Advanced.
Open the Network tab.
In 'Connections' area click 'Settings' button.
Select Manual Proxy Configuration radio button.
In the necessary proxy field(s), put the same settings in the HTTP field then
Click 'OK'