ICS attachments

I receive .ics (icalendar) attachments in my Thunderbird email. How do I go about adding them to my Lightning calendar please? I tried saving them to my Desktop, and then importing, but that didn't do anything. (see also http://goo.gl/z5urw) Or is this a feature that doesn't work with portable Thunderbird?

Anyone else having this sort of issues?

(Running Thunderbird 3.1.10 with Lightning 1.0b2 in Win7 x64.)