Please note that if you wish to explore the catalog you don't need to download it in order to do so, but instead you may use the menu above to navigate the content. This download (large ZIP file), is meant to be used when you require access to the catalog with no Internet conection (like in a field trip), for which you will need to decompress it and then open index.html.
I undestand that I can explore the catalog without this ZIP file and I would like the download button to be enabled.