After updating to Thunderbird 45, QuickText templates are now missing

Today I noticed my QuickText entries had gone missing. After Googling a bit, it appears the problem started happening for some people back in July 2015. There were two recent message threads about this problem on the web site of the original author:

I read though all those threads. Eventually I found a separate web site by rkent, who fixed the problem back in 2015:

In the end, the solution was easy. I  had to download the latest version from the Mozilla add-ons page and install it inside of Thunderbird:

Last modified: July 04, 2016