Hello,

under Linux if I use
webbrowser.open_new('...') a konqueror gets invoked. At the time when invoking konqueror (maybe you probe first, but anyways) you assume that user has a properly installed kde. But if you assume the user has a properly installed KDE you have a better opportunity to open a webpage, even in the browser preferred by the user -- no matter really what it is. Try this one:
kfmclient exec http://sourceforge.net/
using this one the client associated with .html in kcontrol gets invoked.
I suppose that (becouse of the ability to customize the browser) this way would be better if available than guessing which browser would the user prefer.