For some reason, finding the Mozilla Thunderbird calendar add-ons that are compatible with 64-bit Linux were not as easy to find as I thought they would be. It took me several Google searches to finally turn up this link: http://releases.mozilla.org/pub/mozilla.org/calendar/lightning/releases/1.0b2/contrib/linux-x86_64/ When I went to either the Lightning install page or the Provider for Google Calendar install page to get the extensions, it was always an incompatible 32bit version. When I attempted to install those versions I would get an error that said, “Lightning could not be installed because it is not compatible with your Thunderbird build type (Linux_x86_64-gcc3). Please contact the author of this item about the problem.”
P.S. I now noticed that there is an Ubuntu help page on where to find the correct versions. Not sure how that didn’t come up in my searches before. Or maybe I just overlooked it since it’s a bit buried in the page. Not sure.