Not that I am aware of. But your talking about a single freeze. "Have you actually started the program more than once? Allowed it 5 minutes for your anti virus to scan the new program and get over it's huff that you installed something new etc.

I have rebooted the system and started T-Bird many times, with the same result. T-Bird seems to be broken. Prior to the update, everything was fine.

I am using the Norton Security Suite. It didn't "complain" during the T-Bird update download/install. Whenever it gets into a "huff", it will display the cause.

You may not like my colloquialism of the antics of anti virus software. But nothing could be further from the truth about Norton.

New versions of Thunderbird are almost always blocked from accessing the internal without any for of wanting or notification. Changing the firewall rule for Thunderbird to always appears to fix this continuing Quirk with this market leading software. Another side effect is all the files in the profile that Thunderbird tries to access being locked by Norton for up to 10 minutes each while it scans them.

Restarting Windows in Safe mode with networking you will probably not see the freezing or other issues as Norton is not active in that startup mode. As a diagnostic is is a fairly conclusive indication of the cause of the freezing. Safe Mode loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 8, Windows 7, Windows Vista, Windows XP, OSX So try it and see if things work better.

Matt, you're right about the Safe Mode w/ networking: T-Bird works fine there. Evidently Norton has a problem and didn't informed me. Norton never prevented T-Bird before this latest version.

I will change/add a firewall rule that "tells" Norton to leave T-Bird be.  Thanks for your advice, very much appreciated.  Especially so  because I think T-Bird is the best email client out there  --- and I have tried a few.

it may well be you need to add an exception in the real time scanner for the Thunderbird profile. See the notes on Norton here for a link to the exclusion instructions https://wiki.mozilla.org/Thunderbird:Testing:Antivirus_Related_Performance_Issues#Problem_Antivirus_and_Anti-Malware_Packages

None of these suggestions solved this problem. So, in the interest of time, I restored the T-Bird files from a backup of three weeks prior. Now I again have a great email client --- but not with the latest fixes and improvements -- and problems. Thanks very much for your help, but I must move on.