Update:

I restored my profile. I created a new app-specific password at Fastmail, then entered it into saved passwords in Thunderbird. Thunderbird still asks for re-authorization and still displays a blank page.

I deleted the account again, disabled setting up new accounts with the account hub, and re-created my account manually. Thunderbird still does not connect to Fastmail. It has crashed twice (still in Macintosh safe mode) during my efforts.

TROUBLESHOOTING INFORMATION

 Application Basics

   Name: Thunderbird
   Version: 136.0.1
   Build ID: 20250317195841
   Distribution ID:

   Update Channel: release
   User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:136.0) Gecko/20100101 Thunderbird/136.0.1
   OS: Darwin 24.4.0 Darwin Kernel Version 24.4.0: Fri Apr 11 18:32:43 PDT 2025; root:xnu-11417.101.15~117/RELEASE_ARM64_T8103
   OS Theme:
   Rosetta Translated: false

   Multiprocess Windows: 0/0
   Fission Windows: 0/0
             Enabled by default
   Remote Processes: 0
   Enterprise Policies: Inactive
   Google Location Service Key: Missing
   Google Safebrowsing Key: Missing
   Mozilla Location Service Key: Missing
   Safe Mode: true
   Memory Size (RAM): 16.0 GB
   Disk Space Available: 737 GB

 Mail and News Accounts
   account1:
     INCOMING: account1, , (imap) imap.fastmail.com:993, 3, 10
     OUTGOING: , smtp.fastmail.com:465, 3, 10, true
     OUTGOING: , smtp.fastmail.com:465, 3, 10, false
     OUTGOING: , smtp.fastmail.com:465, 3, 10, false
     OUTGOING: , smtp.fastmail.com:465, 3, 10, false
     OUTGOING: , smtp.fastmail.com:465, 3, 10, false
     OUTGOING: , smtp.fastmail.com:465, 3, 10, false
     OUTGOING: , smtp.fastmail.com:465, 3, 10, false
     OUTGOING: , smtp.fastmail.com:465, 3, 10, false
     OUTGOING: , smtp.fastmail.com:465, 3, 10, false
     OUTGOING: , smtp.fastmail.com:465, 3, 10, false
     OUTGOING: , smtp.fastmail.com:465, 3, 10, false
     OUTGOING: , smtp.fastmail.com:465, 3, 10, false
     OUTGOING: , smtp.fastmail.com:465, 3, 10, false
     OUTGOING: , smtp.fastmail.com:465, 3, 10, false
     OUTGOING: , smtp.fastmail.com:465, 3, 10, false
     OUTGOING: , smtp.fastmail.com:465, 3, 10, false
     OUTGOING: , smtp.fastmail.com:465, 3, 10, false
     OUTGOING: , smtp.fastmail.com:465, 3, 10, false
     OUTGOING: , smtp.fastmail.com:465, 3, 10, false
     OUTGOING: , smtp.fastmail.com:465, 3, 10, false
     OUTGOING: , smtp.fastmail.com:465, 3, 10, false

   account2:
     INCOMING: account2, , (none) Local Folders, 0, 3

   account6:
     INCOMING: account6, , (imap) imap.mail.me.com:993, 3, 3
     OUTGOING: , smtp.mail.me.com:587, 2, 3, true
     OUTGOING: , smtp.mail.me.com:587, 2, 3, false

 Libraries

     Library
     Status
     Expected minimum version
     Version in use
     Path

       RNP (OpenPGP)
       OK
       0.17.1
       0.17.1.MZLA.136.0.1.botan
       /Applications/Thunderbird.app/Contents/MacOS/librnp.dylib

       OTR
       Failed to load. OTR chat encryption will not work.
       -
       -
       -

 Calendar Settings

   Home

     Name
     Value

     Name:
     Type: storage
     Disabled: true
     Username:
     URI:
     Refresh Interval:
     Read-only:
     Suppress Alarms:
     Cache Enabled:
     iMIP Identity: id1
     iMIP Disabled:
     iMIP Account:
     Organizer Id:
     Force Email Scheduling:
     Popup Alarms Supported:
     Alarms on Invitation Supported:
     Max Alarms Per Event:
     Attachment Supported:
     Max Categories:
     Privacy State Supported:
     Priority Supported: true
     Event Supported:
     Task Supported:
     Local Time Supported:
     UTC/GMT Supported:
     Auto-Scheduling Supported:

 Crash Reports for the Last 3 Days

 Remote Processes

   Type: Count

 Add-ons

     Name
     Type
     Version
     Enabled
     ID

       System theme — auto
       theme
       1.4.1
       true
       default-theme@mozilla.org

       German Dictionary, extended for Austria
       dictionary
       2.1
       false
       de-AT@dictionaries.addons.mozilla.org

       changeQuote
       extension
       1.8.2
       false
       changequote@caligraf

       ImportExportTools NG
       extension
       14.1.8
       false
       ImportExportToolsNG@cleidigh.kokkini.net

       ReFwdFormatter
       extension
       2.136.0
       false
       refwdformatter@masahiko.info

       Dark
       theme
       1.3
       false
       thunderbird-compact-dark@mozilla.org

       Light
       theme
       1.3
       false
       thunderbird-compact-light@mozilla.org

 Security Software

   Type: Name

     Antivirus:
     Antispyware:
     Firewall:

 Legacy User Stylesheets

   Active: true
   Stylesheets: userChrome.css, userContent.css

 Graphics

     Features
     Compositing: WebRender (Software)
     Font Visibility Debug Info: macOS PlatformmacOS 15.4.1
     Asynchronous Pan/Zoom: wheel input enabled; scrollbar drag enabled; keyboard enabled; autoscroll enabled; smooth pinch-zoom enabled
     WebGL 1 Driver WSI Info: -
     WebGL 1 Driver Renderer: WebGL is currently disabled.
     WebGL 1 Driver Version: -
     WebGL 1 Driver Extensions: -
     WebGL 1 Extensions: -
     WebGL 2 Driver WSI Info: -
     WebGL 2 Driver Renderer: WebGL is currently disabled.
     WebGL 2 Driver Version: -
     WebGL 2 Driver Extensions: -
     WebGL 2 Extensions: -
     Target Frame Rate: 60

     GPU #1
     Active: Yes
     Vendor ID: 0x106b
     RAM: 0

   GPU #2

     Diagnostics
     AzureCanvasBackend: skia
     AzureContentBackend: skia
     AzureFallbackCanvasBackend: skia
     CMSOutputProfile: (REMOVED TO MEET CHARACTER LIMIT)
     Display0: 4480x2520@0Hz scales:2.000000|2.000000
     DisplayCount: 1
     Window Device Pixel Ratios: 2
     Font Visibility Debug Info: macOS PlatformmacOS 15.4.1
     WebGPU Default Adap

Update

I tried to create a new profile. Thunderbird did not respond when I clicked on about:profiles. I re-started in troubleshooting mode and was able to create a new profile and set up my Fastmail account.

Thunderbird has frozen twice and required me to force quit it. I just updated it from 136.0.1 to 138.0 with the hope that 138.0 will not have these problems. But the evidence suggests that the problem lay in my profile, not in Thunderbird's code. Do profiles become corrupted?

Now, I want badly not to re-set all my settings, including config editor changes. Is it possible to copy settings into the new profile?

Sad to see you've received no useful responses. Did the full rebuild work?

I have what I believe is the same problem. I'm on a PC and trying to set up a new account. I don't see where the old manual setup options are, so maybe the only way is to use the "Account Hub."

I put in the full name and the e-mail address and it is "Looking up configuration" and spinning circle for at least 10 minutes till I kill the process entirely. I don't see where it would look up a configuration, as I think my domain provider requires that I'm logged in before disclosing configuration info. But since I have not provided TB with the password yet, TB is not logged in.

I got around my problems by re-creating my profile manually, which was unpleasant.

You may be experiencing one of the problems that I had. Account hub is buggy. I think that someone said fixes are coming. But for now, go into Thunderbird (not account) settings > General > and uncheck the account hub option. Then you will be able to set up accounts the old-fashioned way.

Did you mean to mark this problem as solved?

"Thunderbird (not account) settings > General > and uncheck the account hub option."

OK, that is the missing piece here! Thank you. That ever so important "password" field is now accessible.

[However, that might not be a solution to the original problem. I did not mean to mark this as "solved" - I am not sure how I marked it as solved or how to unmark it as unsolved.]

Konrad, is your problem solved??