The beta version before 92b1 was 91b6, but since the release version 91 is available, you might as well install it instead of an old beta. Best to create a new profile with 91, but if you must attempt to use the 92 profile, launch 91 from a Run window with <path to 91 exe>thunderbird.exe -p --allow-downgrade and choose the profile that was used in 92.

Thanks for the help. I am back in action (v 91 with previous profile) although TB does often hang when I go into Preferences (Task Manager reports it is chewing through RAM and CPU). I wish there was a repair option as MS Office and other progs have. My biggest concern is losing the tags - themselves stored in prefs.js I know but I am concerned how I would recover from a future issue. I have four account records with a dozen tags and several hundred tagged messages, is there any way of backing up the message headers so that if I had to create a new profile I would be able to regenerate them ?

It's fairly easy to set up the tag definitions if necessary, but maintaining the tags on tagged messages depends on if the IMAP server supports keywords. If it does, syncing with the server in a new profile will show the tags. Otherwise, messages will have to be re-tagged, as the tags are stored in the msf index files, which are rebuilt at the first syncing with the server. If the server doesn't support keywords, and tags aren't retained, one option is to sort messages into separate folders, instead of marking them with tags.

Note, downgrading is not recommended, because there are sometimes "upgrades" made to data structures which are not reversible - calendar and addressbook data for example.

spellcheck should be fixed soon we hope, but it depends on some firefox code being resolved. Until then spellcheck on send could be disabled, and rely instead on spellcheck as you type.

Regarding the preferences problem, you are the fourth or fifth person to mention it. We'd like to figure it out, but we need data. So it would be helpful if you a) don't attempt anything corrective/destructive b) work with us to figure out the cause, here or in a bug report https://bugzilla.mozilla.org/enter_bug.cgi?product=Thunderbird

I'm happy to work with you to resolve this issue. This is live data though i.e. I would be well shafted if I had to try to re-tag everything; moving to a single folder is tricky as tagged messages are referenced in more than one folder. I have exported my address book so am not too fussed about that.

I'm not sure whether I would be introducing corruptions if I killed a hanging TB, but the hanging does seem to take no less than 30 minutes to resolve - if it ever does. My profile folder is 43 GB although the backup copy of that folder from before I upgraded is half that size.

On the IMAP server keyword matter, three of my addresses resolve to imap.gmail.com and one to imap.zoho.com

Another point is that now I am on release 91.0.1 (64-bit) I no longer have the issue.

Sorry, I don't mean that I actually need your data. What I mean is we need to gather information by testing hypothesis about the possible cause. It may be a day or two til I get back to you.

I'm hoping it will be fixed next Thursday/Friday with something like 92.0b5. Please post an update at that time.