Select an account in the Folder pane that has messages filtered to other folders.
Click "Manage message filters" in Account Central.
Click the "Filter Log" button.

The filter log dialog is empty.

The filter log should have entries in it.

Additional information.
Go to the Config Editor.
Toggle "browser.tabs.remote.autostart" to "false".
Restart Thunderbird.

The filter log is now populated with entries.

Discourse Topic

It's easy to fix the filter log, and I'll post a patch for that in a minute.

The junk log on the other hand is difficult because of where it is in the UI. Because we load junkLog.xhtml (a chrome: page) as a subdialog in the preferences tab, it can't contain a browser displaying the log (a file: page). Potential workarounds:

• load junkLog.xhtml as a real dialog
• load just the log file as a preferences tab subdialog or as a new tab
• parse the log file and recreate it for display somehow
• give the log a chrome: or about: URI somehow, but this is probably not a good idea

I'm leaning towards the first.

On top of this, it really doesn't help that the junk log file is not written to disk until Thunderbird exits.

Okay, I just did the first option. It seems like the best option to me.

Pushed by mkmelin@iki.fi:
https://hg.mozilla.org/comm-central/rev/77d00abe1e1f
Fix display of filter and junk logs. r=mkmelin

(In reply to Geoff Lankow (:darktrojan) from comment #2)

It's easy to fix the filter log, and I'll post a patch for that in a minute.

The junk log on the other hand is difficult because of where it is in the UI. Because we load junkLog.xhtml (a chrome: page) as a subdialog in the preferences tab, it can't contain a browser displaying the log (a file: page). Potential workarounds:

• load junkLog.xhtml as a real dialog
• load just the log file as a preferences tab subdialog or as a new tab
• parse the log file and recreate it for display somehow
• give the log a chrome: or about: URI somehow, but this is probably not a good idea

I'm leaning towards the first.

On top of this, it really doesn't help that the junk log file is not written to disk until Thunderbird exits.

Should the problem with the Junk log be a different bug and if so what component?

Which problem? The UI problem (although I "fixed" it) would be under Thunderbird::Preferences, the actual logging itself I think goes under MailNews Core::Filters.

Actually the Discourse topic was about the Junk log, and I added the Filter log when I reported the bug.

The Filter log is still empty with e10s enabled in the 86.0b2 candidate tested on Windows 10 and Fedora 33 Workstation.

Comment on attachment 9200605 [details]
Bug 1690042 - Fix display of filter and junk logs. r?mkmelin

[Approval Request Comment]
Regression caused by (bug #): fission
User impact if declined: logs aren't displayed
Testing completed (on c-c, etc.): landed 5 days ago
Risk to taking this patch (and alternatives if risky): no

Comment on attachment 9200605 [details]
Bug 1690042 - Fix display of filter and junk logs. r?mkmelin

[Triage Comment]
Approved for beta

Thunderbird 86.0b3:
https://hg.mozilla.org/releases/comm-beta/rev/21437c4ede93

Filter log works with TB 86.0b3 on Windows 10.