Ok, below is the post I started, until I got a brainstorm. Yes, it happens to me a lot, and once in a while it's even useful. I just looked into the new data folder, picked out a name of one of the files and did a search for it. First try, all I came up with was the new files. But there was an option on the advanced search that would search non-indexed folders, although it warned this may take longer. So, I figured since I couldn't find the folder the help file said should exist, maybe it was one of these 'non-indexed' folders. Whoa - there it was. So, I just right-clicked, chose 'open location' and copied the folders over to the new, backed up location. And when I opened up Thunderbird again, there they were, all my lost emails. WHEW!
If you ever change the path of any data file, be sure to write down the old path before you do. On my old computer I used Microsoft Outlook to access my myriad of email addresses, but with the new computer I got the watered down version of Office 2007 - no Outlook. So, I installed Mozilla Thunderbird, a free Outlook type email program. I've know a lot of people who have used it, and they all liked it, and so far I've had no problems with it. Well, except for one. I wanted to change the data file to a folder that I have automatically backed up - trying to learn from past mistakes. It all worked fine and dandy, except it didn't move over all the old data - I lost all my old emails. So I tried to set it back to the default, and even tried to find the old data file so I could move it to the new location. Yeah, uh, not so much. It didn't exist where the help file told me it should.