Windows and Mac users can safely upgrade to Thunderbird 24.0.1!
Not recommended, I know, but I need Lightning as well, and there are always a few days after a Thunderbird update during which it happily declares Lightning could not be used with this new version of Thunderbird. I keep reading that Mozilla abandoned Thunderbird and Lightning, but that doesn't appear to be the case, although they don't seem to promote it on their web site.
So my idea was to go from "automatic" updates to "ask" and do this manually only if Lightning was available for the new Thunderbird release. Question 1 - How can I stop Thunderbird from updating? Question 2 - Right now, there is a Lightning 4.0.6 version listed to be compatible with TB 38.6.0, but it has no download link at [https://developer.mozilla.org/en-US/docs/Mozilla/Calendar/Calendar_Versions]. Sorry for the confusion - my fault: I am using an external drive with the TB data on different computers which had different TB versions installed. Getting all computers to TB 45.0 hopefully will solve it.
I have Ubuntu 10.10 installed on a Thinkpad machine. The installation was successful, thanks to this very helpful guide.
If you are using Thunderbird 24.0.1 on Linux, you MUST use Lightning 2.6.1.
Thunderbird 24.1.0 (no typo) will be released soon, you MUST use the upcoming Lightning 2.6.2 here.
To date it has not been reviewed by the Mozilla Addons Team, but you can still get it manually using the Other Versions page. On Linux, it is compatible ONLY with Thunderbird 24.0.1, so go ahead and upgrade now.