Ok I have no idea what your talking about, and I suggest no one else does either.

There have been some issues with the conversion to using XULstore.json to cache folders and deleteding the file fixes it. But what your describing sounds like complete hard dusk corruption, perhaps caused by security software. But I would suggest certainly requiring you to run chkdsk over the driver to correct the corruption.

My last point first: Thunderbird updates itself periodically but without asking first. What seems to have happened here is a more radical update than before. Context is essential and I probably missed out key info, like the fact that when I started using Thunderbird some years ago I imported my email archive from Outlook Express. So in the left hand pane, below 'local folders', I could see all my old email folders under the heading 'Outlook Express Import'. What happened yesterday was that all those folders just disappeared, and Thunderbird had a slightly new look, as it sometimes does following its unasked for updates. When I checked my Thunderbird email directory, alongside my original one, a new one had been created, with the basic set of email folders, all empty. I could not delete this directory, so renamed it to get it out of the way. Then I uninstalled and reinstalled Thunderbird and copied back my historic emails into the directory that Thunderbird had created for email - and that worked in the end. If you want I could get you the full directory pathnames.

And another thing: the Thunderbird update has lost my address book.

I ran chkdsk. No problems. What happened here was as a result of Thunderbird updating.