Rated 5 out of 5 stars

Try this:

http://ftp.mozilla.org/pub/mozilla.org/calendar/lightning/tinderbox-builds/comm-beta-win32/1419527852/lightning-3.7.en-US.win32.xpi

You can find appropiate win64 and linux versions as well. Just navigate to the corresponding folder.

Linux 64 bit:
http://ftp.mozilla.org/pub/mozilla.org/calendar/lightning/tinderbox-builds/comm-beta-linux64/1419527852/lightning-3.7.en-US.linux-x86_64.xpi

Works fine here.

HTH

This review is for a previous version of the add-on (3.3.2).  This user has other reviews of this add-on.