I solved the problem, I believe, but not until I wasted a lot of time. By the way, another problem which had shown up was that only one account header files had become, repeatedly, corrupted. Being my default account, I was, obviously very irritated. But, I deleted the account, and then created, again. Of course, I had to struggle with the program which repeatedly gave me the incorrect server, or could not figure one put,until I stopped the scanning, changed from IMAP to POP, reset the server name, and replaced the port number. Incredibly, this was done because a number of people were clueless about their set up. Thanks a lot Mozilla!
After removing that account, everything started working smoothly. Since the header files were becoming corrupted, giving me up to six copies of the same e-mail, I could not do a thing, because the download process was taken several minutes. After I figured out how to get around TB non existent servers, everything seems to work ok. I, then, copied the Inbox from the removed account, and pasted into the newly created one. I was back to square one, until, I found out that all SMTP settings had been changed to the incorrect server.
I, still, dislike TB 3.1.x, but I can use it. And, back to 220.127.116.11, just in case. By the way, I had to change my SMTP, in 3.1.7 to separate authenticated servers, while I could send e-mail in 18.104.22.168 with a single unauthenticated server.
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:22.214.171.124) Gecko/20101203 Firefox/3.6.13