Hi Antonio
i am not sure in understand your question.
Shellexecute API can open an url (with the associated application, here the default browser).
no need to fetch the browser location,its public ).

&&shellexecute
DECLARE INTEGER ShellExecute IN SHELL32.DLL INTEGER nWinHandle,;
                                            STRING cOperation,;
                                            STRING cFileName,;
                                            STRING cParameters,;
                                            STRING cDirectory,;
                                            INTEGER nShowWindow
result = ShellExecute(0, "open", "http://msn.com","","",1)  &&navigator by default (what you want ?)
*result = ShellExecute(0,  "open", "iexplore.exe","http://msn.com","",1)  &&IE
*result = ShellExecute(0, "open", "firefox.exe","http://msn.com","",1)    &&Firefox
*result = ShellExecute(0, "open", "chrome.exe","http://msn.com","",1)     &&chrome