Daiki Ueno <ueno(a)unixuser.org> writes:
 The immediate cause is that set-text-properties calls for the 
 [0, 0] range of the current buffer in browse-url-url-at-point 
 when there is no URL text around point.
 (defun browse-url-url-at-point () (let ((url (thing-at-point 
   'url))) (set-text-properties 0 (length url) nil url) url))
 GNU Emacs's set-text-properties, however, doesn't fail in the 
 same situation.  I don't know which is a better place to fix the 
 symptoms, fsf-compat/text-props.el or browse-url.el. 
IMHO the better solution is to make `set-text-properties' 
consistent with Emacs.  I couldn't find fsf-compat/text-props.el 
though, so I'll leave it to someone else to explore.