It's not loading anything for me. Just stuck with the little icon in the bottom right corner. Other people are having the same issue
There's a certificate error. Go to %localappdata%\Uber Entertainment\Planetary Annihilation\PAMM\resources\app\assets\js\pamm-api.js Near the top you should see two urls. Change the one that's an HTTPS to an HTTP.
You're not sending any data to this site or receiving sensitive data; it's just a JSON file listing all mod information (you can see it here: http://pamm-mereth.rhcloud.com/api/mod). The issue looks like it's resolved, in any case.