I couldn't tell you why but the pictures (jpegs) won't display in the preview in Chrome for me. But you can right click them. Then left click "download" and you should be able to left the file at the bottom of your window once it downloads. I went to the mail box and I had to download it to see a photo.
I don't know if Cura displays STP files. But you should be able to drag an STL file in there no problem.
See if this helps and let me know if it doesn't!