Expand/Collide feature can not be used in mozilla firefox. A javascript error occurs (like img4 not found) when expandable list item clicked.
A solution I create is as follows:
I made changes in locallib.php under scorm directory:
I changed code at line 1348: which is
$result->toc .= '<a href="javascript:expandCollide(img'.$sublist.','.$sublist.','.$nextsco->id.');">
into
$result->toc .= '<a href="javascript:expandCollide(\'img'.$sublist.'\','.$sublist.','.$nextsco->id.');">

I add a line after line 1440:
which = which.substring(0,4);
to get rid of single quote ( ' ) beginning and end of the name

I changed the line 1447:
which is
which.src = "'.$scormpixdir.'/plus.gif";
into
document.getElementById(which).src = "'.$scormpixdir.'/plus.gif";

and line 145:
which is
which.src = "'.$scormpixdir.'/minus.gif";
into
document.getElementById(which).src = "'.$scormpixdir.'/minus.gif";

After mading these changes it works fine on IE and firefox.
If my description above is not clear please contact me to explain in again.