If you did not deliberately download and install v78, then a third-party software updater is running on your system and is responsible for installing it, because v78 IS NOT YET getting offered as an update to v68 users. You need to find what is responsible for installing v78 and TAKE CONTROL of it. Popular antivirus programs like Avast and Kaspersky have a software updater module which DOESN'T adhere to your Tbird update settings.

Open Config Editor, find the preference named "ui.systemUsesDarkTheme" and set its value to 0. This will force Tbird to use a light theme (white or light background color with black or dark foreground colors). A selected folder should be highlighted when you're viewing its contents, so what you're describing is NOT standard behaviour in v78. The config editor tweak will hopefully fix that too, so kindly tone down the rants. While I understand your sentiments about v78, no one desires helping you via a virtual shouting match. See https://support.mozilla.org/questions/1301521

I had a long response entered here, among other things apologizing for my rant. And then before saving the response, I clicked on the Solved button and all my text here disappeared. I'll try to recap for you, as an FYI. 1. I thought I had Tbird set to notify me of available updates but to let ME do them. After the update to the faulty version, checking under Options showed that it was set to do auto updates. Is that the default setting and will I have to reset to my preference after each update? My PC shows that I downloaded and installed version 78.1.1 manually on 8/20/2020. 2. When it did the update automatically, I had double clicked on the desktop icon, and as Tbird was opening, a message displayed that appeared to be generated by Tbird saying "Thunderbird is installing your updates and will open .....". After that, ALL unread messages were shown at the bottom of the Subject and Correspondents columns but with only green dots and no text at all until I clicked on each individual green dot. Further checking and trying out different settings under View produced totally disorganized order and appearance of the messages. It was as if Tbird had lost its mind. 3. Firefox is the only app I have that I let update automatically other than my AV software and Driver Easy. I have no AV or other software that does or forces automatic updates on other programs. Glary Utilities notifies me when updates are available and I then do them manually. This lets me keep up-to-date versions of most programs in my Download folder. 4. Repairing Tbird required two system restores using Macrium Reflect and also uninstalling one of my AV programs. After the second system restore with the AV program (Comodo Cloud free AV) reinstalled, Tbird version 78.1.1 magically opened just like it used to and I then reset to my preference to let ME do the updates. I also use Malwarebytes Pro and I do a daily scan in addition to the live protection, so I THINK my PC is clean. 5. Bottom line: I have no clue what happened, but thank goodness I do a daily backup using Macrium Reflect.

Thanks for your help Stans. I WILL keep your email for future reference.

By the way, you could use a note taking program that saves changes automatically, to draft your responses for online forums, then copy and paste when you're ready to submit. I use the Windows 10 inbuilt/native Sticky Notes app a lot as a "scrap" book exactly for that.