Hey Dave,
That’s pretty accurate but I re-partitioned my hard drive because I didn’t initially setup enough space in the root partition and, after a year or so, started getting messages about lack of space. I was running Mint 19.2 and I always apply all of the recommended updates in Update Manager. That’s why I was surprised when, after reinstalling 19.2, I had the problem with Thunderbird. I had seen the posts about TB 68.2.2 but, as it didn’t come up in Update Manager, I didn’t try to install it and I know that I was on some earlier version than that one.
I found a pre-68 version on Directory Listing: /pub/thunderbird/releases/ and grabbed one labled as a release 67.x - I didn’t realize that the ‘b’ in the name meant that it was a beta version. I nervously installed it, swapped the profile name to my saved profile in a backup of .thunderbird and, it worked! Then, Thunderbird updated itself to the newer Beta version of 72.01b.
I did find that the data is backwards compatible to a release version using “thunderbird -P --allow-downgrade” (see website: How to switch update channel from beta to release | منتدى دعم Thunderbird | Mozilla Support) but, I think I’ll use this version for awhile until I get brave again. It’ll probably be awhile. 
Nervous?? Nah. This is me preparing to wipe my hard drive, re-install the operating system and see what happens…
Thanks Dave and Akito for your help!!!
Wgberninghausen, thanks for looking and your reply. I currently have too many different email addresses to use the web for each one.
Best,
Jim