What's the result of running Windows in safe mode?

@sfhowes, the only difference I could detect when running Windows in safe mode was that there was less 'Sending login information' progress indicated on the status bar near the "Unread" counter.

Tried TB in safe, offline, and normal modes and the result is the same -- after entering the primary password and attempting any further interaction with the UI, "Not Responding" is the result. I captured Task Manager screens from 'normal' mode operation (whilst in Windows Safe Mode).

Hmmm... I did detect that a change to the TB installation directory (from 32-bit to 64-bit) must have taken place in the last couple of months. I found a now-obsolete TB shortcut (dated 07-Sep-2021) in C:\ProgramData\Microsoft\Windows\Start Menu\Programs that pointed to TB in C:\Program Files (x86)\Mozilla Thunderbird, not in C:\Program Files\Mozilla Thunderbird, where the executable is currently located. There is a 'Mozilla Thunderbird' shortcut (dated 29-Nov-2021) that points to the active exe.

Thanks for your attention.

TB seems to install the 64-bit version in the (x86) folder if the previous 32-bit version was already there. In any case, there is no significant difference in performance between 32 and 64 bit TB, or where the app is installed.

If it's still 'not responding' in Windows safe mode, there are a number of possible sources, with some related to gmail's All Mail folder. I suggest you go through this list and see if there are changes that can make a difference.

Update: Went through the list the list as suggested with main takeaway using webmail UI to purge x0,000s of messages across several accounts (and move 000s out of Inbox), but issue remains.

Even tried accessing TB on an older (Win7) device. It also became non-responsive. It was interesting to see that the %AppData%\Thunderbird\Profiles\mjqpd8v8.default\ImapMail\imap.gmail.com\ directory showed evidence of a folder (via a *.msf file) that indicated the presence of an email folder that had been created through the web UI.

Will try using Profile Manager to create a new profile Profile Manager to create a new profile and restoring my backed-up profile. Also checking the solution from this community backup/restore discussion .

Fwiw, I have a month-old 5.35GB MozBackup .pcv archive and am also creating a new 9.35GB backup using good ol' copy/paste .

I suggest to a) exlude AllMail label from IMAP access in Gmail Webmail Standard View Settings-Labels, b) limit number of messages accessible to IMAP there in Settings-Forwarding, c) limit synced messages to 1 month in Tbird each Acc Settings, d) then Repair each acc's Gmail folder from Tbird RMC menu Folder Properties.

You don't need to keep old messages on your PC, only their headers, and new message bodies for faster search when compiling Unified View.

MozBackup is very old and unreliable with newer versions of Thunderbird. You will want to get a new backup method.

Did you solve your performance problem?

Update: Went through the list .... Will try using Profile Manager to create a new profile Profile Manager to create a new profile and restoring my backed-up profile. Also checking the solution from this community backup/restore discussion . ...

Further Update: Unfortunately, none of the efforts to restore archived profiles were effective, so a rebuild was necessary. Adjusted Gmail account settings per @zamar27 advice and re-installed TB and added "essential" accounts (and add-ons) one by one.

Make sure the 'Firewall' does have 'Thunderbird' as an allowed program.