Can't send or download messages after 31.4.0 update

Question

Auto-update to 31.4.0 on/about Jan 14, 2015 has caused my install to fail sending and receiving messages. Initial program load and subsequent Get Messages requests go nowhere: The progress display in the page footer shows "[acct name]: Connecting to [host name]..." and nothing else happens. When attempting to send a new message, the Sending Message progress box appears, followed by the Send Message Error box containing the warning "Sending of message failed. The message could not be sent because connecting to SMTP server [smtp host] failed. etc."
No changes to my Thunderbird configuration have been made prior to or since the auto-upgrade. When the upgrade occurred I noticed a momentary balloon message in the lower right corner of my display which vanished before I could read it.
I have tried deleting the signon password for the mail server, but on re-try Thunderbird does not ask for a new password. It is going south sooner than that.
Examination of the Error Console shows that, after a series of ordinary start-up entries, two final entries look fishy: (1) "mutating the [[Prototype]] of an object will cause your code to run very slowly; instead create the object... etc." followed by (2) "Could not read chrome manifest 'file:///C:/Program%20(x86)/Mozilla%20Thunderbird/chrome.manifest'." The latter file is indeed absent.
Note: My system is configured to read its profile info from portable drive X:\ instead of the C:\ drive.
I have accessed my mail server via webmail and there are indeed incoming files available to download.

Answer 1

I'm having the same problem as you with really similar symptoms. I'm linking my post here for reference in case it helps. [https://support.mozilla.org/en-US/questions/1041448 Receiving emails doesn't attempt to log in. No errors output.]