Because of the way FF treats Strings (IE casts a result to the right type), Firefox doesn't always work with SCORM packages, ie. scores are not stored.
I suggest the culprit is the code:
elementmodel = element.replace(expression,'.n.');
in the various datamodel files, for example there are 4 occurrences in scorm_12.js.php.
Replacing this with
elementmodel = String(element).replace(expression,'.n.');
makes it "Firefox-compliant"
This is the case for moodle 1.6 through 1.8.
I suggest we make this change to the code, as it surely doesn't affect compatibility with IE.