I can find a letters

I can choose a sender mailbox

But I can not see it in the frame of boxes/folders

Actually, all accounts are present, letters, settings. But folders and accounts in the left frame unavailable - it is empty like on the first picture

Thanks for providing good details.

Please check Error Console immediately after startup for warnings and errors, and post them here. control+shift+J

Please, the screenshot was attached

Thanks for providing good details. Please check Error Console immediately after startup for warnings and errors, and post them here. control+shift+J

In troubleshooting mode turned off add-ons and resisted settings - the same

Your issue matches to https://bugzilla.mozilla.org/show_bug.cgi?id=1869685.

Which does not yet have a fix attached to it. But perhaps this will be resolved by https://bugzilla.mozilla.org/show_bug.cgi?id=1870817

Can I install older version of Thunderbird? Where I can get it to reinstall. few versions older, because it worked perfect

I have reinstalled a new version with a new profile I can see the mailbox and its folder. As soon as I start to import from the LIbrary my Thunderbird 11,5 GB mailboxes - I have the same problem with empty tab.

Please try this and report back on results. On the original profile....

In Thunderbird

• Help > Troubleshooting Information
• Under 'Application Basics' half way is Profile folder - click on 'Open Finder'

A new window opens showing contents of profile name folder.

• Exit Thunderbird now.

• Locate the file called 'folderCache.json'
• Please rename this file as 'folderCache.json.old' - so you still have it but it's just not going to be used.

Thunderbird will create a new one when you restart.

• When you want to start Thunderbird - use the right click on Thunderbird shortcut and click on the 'Run as administrator' option - I'm using Windows OS - not sure what you see on a Mac. I'm not suggesting you use that method of starting as a rule from now onwards - just this once.

Please report on results.

I have reinstalled a new version with a new profile I can see the mailbox and its folder. As soon as I start to import from the LIbrary my Thunderbird 11,5 GB mailboxes - I have the same problem with empty tab.

Are you referring to Tools > Import?