The Oni Mod Depot is only available without SSL (HTTPS), so you need to access it with http://mods.oni2.net.
If clicking that URL does not work, you'll need to copy-paste it into your browser's address bar.
If that doesn't work either and you're in Firefox, you need to turn off the feature in your browser that forces HTTPS. Currently you should find it at Settings > Security > HTTPS-Only Mode.