You can try making the requests "schemeless"...
Instead of http://www.example.com/styles/ngen_file_field.css
or https://www.example.com/styles/ngen_file_field.css
simply edit to:
//www.example.com/styles/ngen_file_field.css//www.example.com/styles/ngen_file_field.css
This will cause the resources to inherit the scheme of the page in which they are loaded.