User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Firefox/78.0

Steps to reproduce:

Displayed a received message in the preview window.

Actual results:

None of my messages show headers any more.

This is less visible if "normal" headers are shown but becomes more visible when you select "all" headers (see attachment). This happens regardless if the message is opened in a view, tab or window.

Instead, an extension link to "1 more" is sometimes shown, but does nothing.

On a side note: switching headers from "normal" to "all" does not work correctly, wither. After switching, you have to restart Thunderbird to make them show.

Expected results:

The headers should be shown. This works fine up to 69.x. I also tried 79.0b1 and it has the same bug.

I even tried to simplify some messages to minimal headers in my mailbox, but the same thin happened.

Why is that area yellow? Are you using some incompatible add-on, or userChrome.css modifications?

No, the yellow overlay was just an edit to highlight the problem area. I even tried with a fresh install on another machine, there are no mods involved.

Fresh install but the same profile? Could you test a new profile?

Completely fresh install, new profile. I just added the credentials for my IMAP account after installation.

Could it be some problem with the localized version? Do you see the same with an en-US install?
Anything in the error console?

I tried with an english version as well.

However, I just tried again with a new profile and now it works.

The errors in the console seem to point to the address book: AddrBookDirectory.jsm:174

I cannot create new mails as well. The "send" button is always grayed out and the address book is empty.

Found it: Apparently, there were offending entries in prefs.js for some LDAP servers (not that I was aware of ever having them). I deleted all entries starting with 'user_pref("ldap_2.' and now it works again.

I guess this is then just a symptom of bug 1653234.

Yes, I think that the missing headers were only a symptom of a broken address book.

I did not lose my contacts, though. After I deleted the ldap_2 preferences, my address book is back with all contacts.

To test a fix:

1. download and extract https://firefox-ci-tc.services.mozilla.com/api/queue/v1/task/WAxn9pUkSVix7EHar9_6PA/runs/0/artifacts/public/build/target.zip
2. Navigate to the Thunderbird directory and run thunderbird.exe directly from there
3. Please post your results.

After testing, at the point where you want to get back to version 78 or 68, you'll need to use --allow-downgrade at the dos command prompt.

I did that. First I verified that with the ldap_2 entries in my prefs, 78.0 showed the errors again (which it did).

Thunderbird Daily took extremely long to start up (> 20 seconds), only to display a "create new user" dialog. When I interrupted that, I saw a new blank profile, so I tried "thunderbird -p", selecting my old profile.

Lo and behold, Thunderbird Daily did come up and works (i.e. headers are there, address book is functional and mails can be sent).

What do the problematic ldap_2 entries look like?

(In reply to Magnus Melin [:mkmelin] from comment #9)

I guess this is then just a symptom of bug 1653234.

(In reply to Magnus Melin [:mkmelin] from comment #13)

What do the problematic ldap_2 entries look like?

See reporter's comment 14, attachment 9165287 [details].

So would bug 1653234 fix this LDAP server prefs issue?
Do we have/need a bug for TB78 trying to create a new profile (comment 12) instead of using the existing one which worked?

Confirming per reporter's comment 8 and comment 12 where this is semi-fixed, maybe by bug 1653234 (but still requiring manual intervention to use existing profile).

Confirming per reporter's comment 8 and comment 12 where this is semi-fixed, maybe by bug 1653234 (but still requiring manual intervention to use existing profile).

(In reply to Thomas D. from comment #15)

So would bug 1653234 fix this LDAP server prefs issue?

Yes they should no longer cause a problems.

Do we have/need a bug for TB78 trying to create a new profile (comment 12) instead of using the existing one which worked?

I doubt it. Sounds like install in another folder -> profile per install triggered.

Thanks. Resolved per reporter's comment 12 and mkmelin's comment 18.