The malware site seems to be down now.
In this case, it would not download a .exe file. Instead, it would tell you that you didn't have the right browser plugin to see the Christmas card, and would start the process of installing a plugin on your browser if you were naive enough to allow it to. On Windows it would install a Browser Helper Object for Explorer, or a plugin for other browsers; on the Mac it would try to install a plugin for Safari or Chrome.