I need an inline browser javascript to detect if the browser is MAC
Firefox and to load a gif. If not mac firefox load an SWF.

eg:

detect if Mac firefox if yes load src="/content/flash/WYD03.gif"

if other browser load src="/content/flash/WYD03.swf"

is this possible?

I would need it to be in the code NOT in the header as there are
several swf's on one page and Mac Firefox is making the SWF on top of
all other divs therefore not displaying the divs.

see the problem here beamcreative.com/menutest.aspx

index does not work with .swf files. I have a work around for all
other browsers but Mac/Firefox has a bug that prevents SWF files to be
at the bottom layer.

Humm.. I think you could search for Browser detection javascript and you will find exactly what you are looking for.

Dynamicdrive.com has many resources like it.