How can I find out why JS isn't shown as executable in Firebug?

Question

I'm trying to debug some JS code, and when it's viewed in firebug, it appears as "not compiled", that is, the line numbers are grey and not green.

I've pasted the code in JSLint, and JSHint, and they do not show any errors.

Here's a sample of the code:

<script type='text/javascript'>
    var fld_def_set = {
        spec_fld_type: {
            ft_cts: {
                fld_cfg: {
                    spec_fld_name: {
                        fd_display: 1,
                        fd_enable: 1,
                        fd_evaldef: 1,
                        fd_def_val: 'fld_prefix + "created"'
                    }
                }
            }        //    end of saddr
        }    //    end of spec_fld_type
    };
</script>

When I view the code in JSHint, it appears that the code has no errors, except for an unused variable warning. Yet in FireFox, the code is not recognized.