When you print from Thunderbird the print dialog appears behind the main Thunderbird window. Of course, it should appear in the front of Thunderbird. You can reproduce it every time.
Mozilla developers say this window is a part of Ubuntu and NOT of Thunderbird.
(Also this window is NOT transalated to German fully - but for this I opened a separate bug already)
ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: thunderbird 1:68.10.0+build1-0ubuntu0.20.04.1
ProcVersionSignature: Ubuntu 5.4.0-40.44-generic 5.4.44
Uname: Linux 5.4.0-40-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.20.11-0ubuntu27.3
Architecture: amd64
BuildID: 20200629235513
CasperMD5CheckResult: skip
CurrentDesktop: KDE
Date: Mon Jul 13 22:29:20 2020
DefaultProfileExtensions: extensions.sqlite corrupt or missing
DefaultProfileIncompatibleExtensions: Unavailable (corrupt or non-existant compatibility.ini or extensions.sqlite)
DefaultProfileLocales: extensions.sqlite corrupt or missing
DefaultProfilePrefErrors: Unexpected character ',' before close parenthesis @ /usr/lib/thunderbird/omni.ja:greprefs.js:1138
DefaultProfileThemes: extensions.sqlite corrupt or missing
InstallationDate: Installed on 2020-07-12 (0 days ago)
InstallationMedia: Kubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
Profiles:
Profile1 (Default) - LastVersion=None/None (Out of date)
Profile0 - LastVersion=68.10.0/20200629235513 (In use)
SourcePackage: thunderbird
UpgradeStatus: No upgrade log present (probably fresh install)
Just tested in a fully up-to-date Kubuntu 20.04 VM (amd64), and I cannot observe the problem. Printing an e-mail does pop up the print dialog in front of the thunderbird window.
Can you share the exact steps you're taking to reproduce the problem? Can you maybe attach a screencast demonstrating it?