SRC Parameter Not Working In Mozilla When Path Is Included

I normally use Mozilla 1.4 on Windows XP Pro.
As I was developing some test webpages, I discovered that the SRC
parameter doesn't seem to work when a path is used with the filename.

In one example, when I want to run a JavaScript from an external file
(i.e., not inline), I would do the following ...

<SCRIPT LANGUAGE="JavaScript" SRC="program.js"> </SCRIPT>

If "program.js" were in a different subdirectory than the .htm file
referring to it, the filename would have to be prefixed by the
pathname as follows ...

<SCRIPT LANGUAGE="JavaScript" SRC="/mydir/program.js"> </SCRIPT>

But when I ran the above from within an .htm file loaded locally into
Mozilla, it did not work. (The result was as if the above code weren't
there). However, when I ran the identical code on Internet Explorer
(v.6), it worked. Code: