[Bug 711305]

[Amanita+bugzilla]

I can confirm the same bug, using Librewolf Flatpak and clicking on a
mailto link.

Thunderbird latest Flatpak from Flathub

--- Software ---
OS: Fedora Linux 38.20230814.0 (Kinoite)
KDE Plasma: 5.27.6
KDE Frameworks: 5.108.0
Qt: 5.15.10
Kernel: 6.4.10-200.fc38.x86_64
Compositor: wayland

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https://bugs.launchpad.net/bugs/711305

Title:
  Thunderbird is already running, but is not responding. To open a new
  window, you must first close the existing Thunderbird process, or
  restart your system. Error received when clicking a mailto link in
  firefox.

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