This is a known issue which should be resolved in the next couple weeks.

Config. editor is under Preferences at the bottom of the General tab (or search Preferences for editor).

Does TB hang in safe (troubleshooting) mode? Hold Shift when launching TB. Is hardware acceleration (Preferences/General/Indexing) enabled in normal mode?

In safe mode Preferences opens OK. Weird because when I manually disable all addons - the hanging problem is still present. Looks like Safe Mode disables something else to avoid hanging. BTW - the theme is system. I have attached the list of addons I am using now (but again: manual disabling all of them does not help).

Safe mode disables hardware acceleration, among other factors, so if it's enabled in normal mode, disable it and restart TB in normal mode.

Nah, disabling hardware acceleration does not help. BTW: Preferences are different in Safe and Normal Modes!

Launch in safe mode, 'Reset toolbars & controls', 'Make changes & restart'.

Your pictures are of two different sections of Preferences.

Didn't help - the same issue. I have shown "Preferences" I see immediately when I go to "Preferences" in different mode. It is very possible different sections are opened by default.

Preferences should open the same way as when TB was last closed. Delete session.json from the profile if it doesn't.

Did you use a profile from an earlier version of TB when 91 was installed? That is the cause of many problems.

If sessions.json is the same - why Safe and Normal mode opens different tabs of Preferences? By the way - there was no sessions.json in profile during experiments mentioned above.

Yes, for sure I am not creating new profile each time Thunderbird releses an update. There are 20 accounts in my Thunderbird + local folders with appropriate settings. Should I recreate settings for them with every update? Definitely no, I really expect updating process is doing something meaningful during "cleaning up the birdcage".

And once again: the problem starts appearing with move to 91 version. I never expected any problem earlier.

I really think to revert back to 78.13.0. Branch 91 seems too crude.

Preferences should open the same way as when TB was last closed. Delete session.json from the profile if it doesn't. Did you use a profile from an earlier version of TB when 91 was installed? That is the cause of many problems.

But again, in this case, there is a known bug that is causing the preference hang. And it is known to NOT be related to the profile. And so recreating the profile is a crappy and utterly useless exercise.

And so the alternative to avoid the situation is simply don't use preferences for a short until the problem is fixed.

Just want to report that 91.1.0 released today is still affected.

If sessions.json is the same - why Safe and Normal mode opens different tabs of Preferences? By the way - there was no sessions.json in profile during experiments mentioned above. Yes, for sure I am not creating new profile each time Thunderbird releses an update. There are 20 accounts in my Thunderbird + local folders with appropriate settings. Should I recreate settings for them with every update? Definitely no, I really expect updating process is doing something meaningful during "cleaning up the birdcage". And once again: the problem starts appearing with move to 91 version. I never expected any problem earlier. I really think to revert back to 78.13.0. Branch 91 seems too crude.

It will take 5 minutes to create a new profile with 91, add an account, and see if the problem remains. I haven't experienced it myself, and haven't seen a flood of reports that would indicate it's a widespread problem. If the test profile shows the same symptoms, you can return to the original profile, which is unaffected by the new one, and wait for a future release that might fix upgrade bugs.

The fact you have no session.json file is a sign that something's wrong with the profile.

In fact I see two different approaches to my case. I'm glad I've got such attention but I'd better wait for error fix as Wayne Mery suggests rather than deep investigation of this error (that was done already I think).

This is a known issue which should be resolved in the next couple weeks.

Are you using an English version of Thunderbird? Or a language pack?

I am using Russian version.

And are you using a language pack?

I am using the version from here: http://download-installer.cdn.mozilla.net/pub/thunderbird/releases/91.1.1/win64/ru/Thunderbird%20Setup%2091.1.1.exe Updates are also performed from similar links. I never install/use any additional langpacks.

This is just to let everybody know that with latest 91.3.0 the problem still exists. Seems Mozilla is very prompt in fixing bugs as always ("next couple weeks", oh yeah...)

Perhaps you confuse Thunderbird with Firefox. Firefox is developedna nd built by Mozilla, Thunderbird is not https://www.thunderbird.net/en-US/about/

Please post the contents of help > more troubleshooting info > copy text to clipboard

In fact I don't care much especially being on support.MOZILLA.org.

   Имя: Thunderbird
   Версия: 91.3.0
   ID сборки: 20211101223011

   User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.3.0
   ОС: Windows_NT 10.0 22000

   Запускающий процесс: Включён
   Многопроцессные окна: 0/0
   Окна Fission: 0/0
             Отключены по умолчанию
   Удалённые процессы: 3
   Корпоративные политики: Неактивны
   Ключ Службы определения местоположения от Google: Отсутствует
   Ключ Google Safebrowsing: Отсутствует
   Ключ Службы определения местоположения от Mozilla: Отсутствует
   Безопасный Режим: false

 Учётные записи почты и новостей
   account1:
     INCOMING: account1, , (imap) imap.yandex.com:993, 3, passwordCleartext
     OUTGOING: , mail.smtp2go.com:443, 3, passwordEncrypted, true

   account2:
     INCOMING: account2, , (none) Local Folders, 3, passwordCleartext

   account3:
     INCOMING: account3, , (imap) imap.yandex.com:993, 3, passwordCleartext
     OUTGOING: , mail.smtp2go.com:443, 3, passwordEncrypted, true

   account4:
     INCOMING: account4, , (imap) imap.yandex.com:993, 3, passwordCleartext
     OUTGOING: , mail.smtp2go.com:443, 3, passwordEncrypted, true

   account5:
     INCOMING: account5, , (imap) imap.yandex.com:993, 3, passwordCleartext
     OUTGOING: , mail.smtp2go.com:443, 3, passwordEncrypted, true

   account6:
     INCOMING: account6, , (imap) imap.yandex.com:993, 3, passwordCleartext
     OUTGOING: , mail.smtp2go.com:443, 3, passwordEncrypted, true

   account7:
     INCOMING: account7, , (imap) imap.gmail.com:993, 3, OAuth2
     OUTGOING: , smtp.gmail.com:465, 3, OAuth2, true

   account8:
     INCOMING: account8, , (imap) imap.gmail.com:993, 3, OAuth2
     OUTGOING: , smtp.gmail.com:465, 3, OAuth2, true

   account9:
     INCOMING: account9, , (imap) imap.mail.ru:993, 3, OAuth2
     OUTGOING: , smtp.mail.ru:465, 3, passwordCleartext, true

   account11:
     INCOMING: account11, , (imap) imap.yandex.com:993, 3, passwordCleartext
     OUTGOING: , mail.smtp2go.com:443, 3, passwordEncrypted, true

   account12:
     INCOMING: account12, , (imap) imap.yandex.ru:993, 3, passwordCleartext
     OUTGOING: , smtp.yandex.ru:465, 3, passwordCleartext, true

   account13:
     INCOMING: account13, , (imap) imap.gmail.com:993, 3, OAuth2
     OUTGOING: , smtp.gmail.com:465, 3, OAuth2, true

   account14:
     INCOMING: account14, , (imap) imap.gmail.com:993, 3, OAuth2
     OUTGOING: , smtp.gmail.com:465, 3, OAuth2, true

   account16:
     INCOMING: account16, , (imap) imap.mail.ru:993, 3, OAuth2
     OUTGOING: , smtp.mail.ru:465, 3, OAuth2, true

   account17:
     INCOMING: account17, , (imap) outlook.office365.com:993, 3, passwordCleartext
     OUTGOING: , smtp.office365.com:587, 2, passwordCleartext, true

   account18:
     INCOMING: account18, , (imap) outlook.office365.com:993, 3, passwordCleartext
     OUTGOING: , smtp.office365.com:587, 2, passwordCleartext, true

   account19:
     INCOMING: account19, , (imap) outlook.office365.com:993, 3, passwordCleartext
     OUTGOING: , smtp.office365.com:587, 2, passwordCleartext, true

   account20:
     INCOMING: account20, , (imap) outlook.office365.com:993, 3, passwordCleartext
     OUTGOING: , smtp.office365.com:587, 2, passwordCleartext, true

   account21:
     INCOMING: account21, , (imap) imap.mail.ru:993, 3, OAuth2
     OUTGOING: , smtp.mail.ru:465, 3, OAuth2, true

   account22:
     INCOMING: account22, , (imap) imap.yandex.com:993, 3, OAuth2
     OUTGOING: , smtp.yandex.com:465, 3, OAuth2, true

   account23:
     INCOMING: account23, , (imap) imap.gmail.com:993, 3, OAuth2
     OUTGOING: , smtp.gmail.com:465, 3, OAuth2, true

 Настройки календаря

       Имя
       Значение

       Имя:
       Тип: storage
       Отключён:
       Имя пользователя:
       URI:
       Интервал обновления:
       Только для чтения:
       Подавление уведомлений:
       Кэш включён:
       Идентификатор iMIP: id1
       iMIP отключён:
       Учётная запись iMIP:
       Идентификатор организатора:
       Принудительное планирование электронной почты:
       Всплывающие уведомления поддерживаются:
       Уведомления по приглашению поддерживаются:
       Максимальное число уведомлений на событие:
       Вложения поддерживаются:
       Максимальное число категорий:
       Состояние приватности поддерживается:
       Приоритет поддерживается: true
       События поддерживаются:
       Задачи поддерживаются:
       Местное время поддерживается:
       UTC/GMT поддерживается:
       Автоматическое планирование поддерживается:

 Сообщения о падениях за последние 3 дня

 Удалённые процессы

   Тип: Количество

     Веб-содержимое: 1 / 8
     Расширение: 1
     GPU: 1

 Дополнения

     Имя
     Тип
     Версия
     Включено
     ID

       British English Dictionary (Marco Pinto)
       dictionary
       3.0.2
       true
       marcoagpinto@mail.telepac.pt

       Ukrainian dictionary
       dictionary
       4.6.2
       true
       uk-ua@dictionaries.addons.mozilla.org

       Википедия (ru)
       extension
       1.0
       true
       wikipedia@search.mozilla.org

       Поиск Mail.Ru
       extension
       1.0
       true
       mailru@search.mozilla.org

       Яндекс
       extension
       1.0
       true
       yandex@search.mozilla.org

       DuckDuckGo
       extension
       1.0
       true
       ddg@search.mozilla.org

       Google
       extension
       1.0
       true
       google@search.mozilla.org

       Manually sort folders
       extension
       2.1.1
       true
       tbsortfolders@xulforum.org

       OZON.ru
       extension
       1.2
       true
       ozonru@search.mozilla.org

       Price.ru
       extension
       1.0
       true
       priceru@search.mozilla.org

       quickFilters
       extension
       5.3.2
       true
       quickFilters@axelg.com

       Quicktext
       extension
       4.1
       true
       {8845E3B3-E8FB-40E2-95E9-EC40294818C4}

       Send Later
       extension
       9.0.6
       true
       sendlater3@kamens.us

       Text Link
       extension
       6.0.2
       true
       {54BB9F3F-07E5-486c-9B39-C7398B99391C}

       Russian (RU) Language Pack
       locale
       91.0buildid20210805011554
       true
       langpack-ru@thunderbird.mozilla.org

       Copy Sent to Current
       extension
       3.12
       false
       copysent2current@ggbs.de

       LookOut
       extension
       1.2.13
       false
       lookout@aron.rubin

       Mail Redirect
       extension
       0.10.9
       false
       {CC3C233D-6668-41bc-AAEB-F3A1D1D594F5}

       MEGAbird
       extension
       3.0
       false
       thunderbird-filelink@mega.nz

       Message Header Toolbar Customize
       extension
       2.2.1
       false
       msghdrcustomize@hogi.sakura.ne.jp

       QuoteAndComposeManager
       extension
       0.4.1
       false
       {ce1c1a31-4ec2-484f-8099-e2cb0f381c21}

       TorBirdy
       extension
       0.2.6
       false
       castironthunderbirdclub@torproject.org

 Графика
     Композитинг: WebRender
     Асинхронное панорамирование/зум: включён ввод колесиком; перетаскивание полосы прокрутки включено; клавиатура включена; автопрокрутка включена; плавное масштабирование жестами включено
     WebGL 1 - Информация WSI драйвера: EGL_VENDOR: Google Inc. (adapter LUID: 0000000000019584)

EGL_VERSION: 1.5 (ANGLE 2.1.14226 git hash: 31a43497be09) EGL_EXTENSIONS: EGL_EXT_create_context_robustness EGL_ANGLE_d3d_share_handle_client_buffer EGL_ANGLE_d3d_texture_client_buffer EGL_ANGLE_surface_d3d_texture_2d_share_handle EGL_ANGLE_query_surface_pointer EGL_ANGLE_window_fixed_size EGL_ANGLE_keyed_mutex EGL_ANGLE_surface_orientation EGL_ANGLE_direct_composition EGL_NV_post_sub_buffer EGL_KHR_create_context EGL_EXT_device_query EGL_KHR_image EGL_KHR_image_base EGL_KHR_gl_texture_2D_image EGL_KHR_gl_texture_cubemap_image EGL_KHR_gl_renderbuffer_image EGL_KHR_get_all_proc_addresses EGL_KHR_stream EGL_KHR_stream_consumer_gltexture EGL_NV_stream_consumer_gltexture_yuv EGL_ANGLE_flexible_surface_compatibility EGL_ANGLE_stream_producer_d3d_texture EGL_ANGLE_create_context_webgl_compatibility EGL_CHROMIUM_create_context_bind_generates_resource EGL_CHROMIUM_sync_control EGL_EXT_pixel_format_float EGL_KHR_surfaceless_context EGL_ANGLE_display_texture_share_group EGL_ANGLE_display_semaphore_share_group EGL_ANGLE_create_context_client_arrays EGL_ANGLE_program_cache_control EGL_ANGLE_robust_resource_initialization EGL_ANGLE_create_context_extensions_enabled EGL_ANDROID_blo