browse-url-default-browser is a compiled Lisp function in `browse-url.el'.

(browse-url-default-browser URL &rest ARGS)

Find a suitable browser and ask it to load URL.
Default to the URL around or before point.

When called interactively, if variable `browse-url-new-window-flag' is
non-nil, load the document in a new window, if possible, otherwise use
a random existing one. A non-nil interactive prefix argument reverses
the effect of `browse-url-new-window-flag'.

When called non-interactively, optional second argument NEW-WINDOW is
used instead of `browse-url-new-window-flag'.