No! I do not think so. You upgraded to Windows 10 and installed Thunderbird and set up your two gmail accounts in your new shiny copy of Thunderbird.. Is that more like what you did?

Have a look for your old Thunderbird profile in the C:\windows.ols folder structure where Microsoft dumped it.

See https://support.mozilla.org/en-US/kb/profiles-tb

C:\windows.ols folder

Where would this be?

typo.. windows.old

Matt, thanks so much. I noticed my Norton security program was not working, and their website said to first try restarting the computer. I did that, and to my surprise, Windows 10 had restored all of my previous programs with their settings, including Thunderbird with the Local folders. Ironically, though, Norton still didn't work. Long story short, while I was "chatting" with their tech support about why I didn't have an account with them to remove and reload Norton, I got a pop up asking me if I wanted to download Norton. I did and it worked. The reason why: I have Fios here in our house in Maryland, but Xfinity in our Florida house. So, even though all three of our computers are here connected to the internet via FIOS, they get the free Norton security program because of my Florida account. Anyway, thanks again for the help.