Insert some URL, e.g. "http://www.gnu.org".
Move point inside the URL.
M-x load-library RET ffap RET
M-x ffap-other-window RET RET
The URL is now opened in the default browser, as expected.  However, the
window is also split, even if the default browser is external (not
EWW).  ffap-other-window should not change the window configuration
unless it has to display a buffer.