On one system make a daemon that listens to requests and opens URLs in a browser.
On the other system set your default browser to something that invokes such a request.
So the first part of this is an HTTP server that listens to requests on the machine where you want to open the browser. On an incoming request it opens (in a browser) the URL given as an argument of a POST request.
You should add this script to startup, it's supposed to run in the background.
The second part is something that invokes the request.
You should designate this script as your default browser.
In KDE: Default Applications → Web Browser
It can also be used as a command line tool:
The Python scripts should work on all major systems with any reasonably recent Python version (I suspect 2.6+, 3.1+).
On Windows, if you don't want a Python script to run in a command window, you should change its extension to
.pyw. Use Task Manager if you want to stop it (look for pythonw.exe).
VirtualBox network adapter should be set to NAT (default setting). More about the IP address here. The choice of port is arbitrary, feel free to change 1337 to something else everywhere.
The server is secure because it listens only to connections from localhost. VirtualBox makes it work somehow. But if you want this to work remotely, specify the listening IP address as
'' instead of