See discussions in bug #1352621 and bug #1338995 for
even more details.

Background:

The webbrowser.py was modified, post-Python 2.4.2, to
tell whether or not the browser invocation succeeded or
not.  Unfortunately, the modifications caused Python
applications to hang when no browser was already
present.    And the reputed fix for bug #1338995,
revision 41419, only made things worse for UnixBrowsers.

Fix:

The changes to webbrowser.py were well intentioned, but
failed because it was difficult to tell if invocation
succeeded due to an extra level of indirection in
invoking the browser by using os.system().

The attached patch, for revision 41511, uses
subprocess.Popen() instead for UnixBrowser.  The other
uses of os.system() would also benefit, but are less
critical to me.