Thunderbird cannot open a new Zen window when clicking a link

[thpar]

Preliminary Checks

• I have read and understood the important section above.
• I have searched existing issues and avoided creating duplicates.
• I am not filing an enhancement request.
• I have checked that this issue cannot be reproduced on Mozilla Firefox.
• I have checked that this issue can be reproduced once I removed all my Mods and Custom CSS.

What happened?

When clicking a link in a Thunderbird e-mail, and no Zen browser window is open yet, a new Zen window opens and immediately crashes. The Zen window is showing, but only shows "your tab has crashed" warning pages and cannot be further interacted with.
The Zen window then needs to be closed, Zen has to be manually opened again, and only then clicking a Thunderbird link opens as expected.

This bug only pops up with the specific combination Thunderbird + Zen browser. Other applications can open Zen without issue and with another default browser, Thunderbird links opens a new browser window as expected.
This could of course also be an issue with Thunderbird.

I am using KDE on Fedora 43, where Thunderbird was installed from the Fedora repo and Zen as Flatpak.

Expected behavior

Clicking a link in a Thunderbird e-mail should be able to launch a new Zen window when none is open yet

Actual behavior

A new window is opened and immediately crashes.

Steps to reproduce

• Open an e-mail in Thunderbird containing a link
• Make sure no other Zen browser window is open yet
• Click the link
• See Zen open and crash

Screenshots and videos

No response

Version

1.18.3b

What platform are you seeing the problem on?

Linux (Flatpak)

What component is this issue related to?

Other

Relevant log output if applicable

When launching Thunderbird from commandline, I see these warnings when the Zen window crashes (interestingly referring to the non-existing directory /home/ubuntu/)

[Parent 2, IPC I/O Parent] WARNING: Failed to launch socket subprocess @FSC::SFNS::Recv (Error:0): file /home/ubuntu/actions-runner/_work/desktop/desktop/engine/ipc/glue/GeckoChildProcessHost.cpp:812
[Parent 2, IPC I/O Parent] WARNING: process 78 exited on signal 11: file /home/ubuntu/actions-runner/_work/desktop/desktop/engine/ipc/chromium/src/chrome/common/process_watcher_posix_sigchld.cc:134
[Parent 2, IPC I/O Parent] WARNING: Failed to launch tab subprocess @FSC::SFNS::Recv (Error:0): file /home/ubuntu/actions-runner/_work/desktop/desktop/engine/ipc/glue/GeckoChildProcessHost.cpp:812

[Parent 2, IPC Launch] WARNING: fork() failed: Operation not permitted: file /home/ubuntu/actions-runner/_work/desktop/desktop/engine/ipc/chromium/src/base/process_util_linux.cc:98
[Parent 2, IPC I/O Parent] WARNING: process 135 exited on signal 11: file /home/ubuntu/actions-runner/_work/desktop/desktop/engine/ipc/chromium/src/chrome/common/process_watcher_posix_sigchld.cc:134

[Propheticus]

Likely caused by the flatpak not having access to your home dir. You can use a tool like Flatseal to manage file system permissions. (Or use a non Flatpak version)

[thpar]

Good guess, but I don't think that's it.

There's a clean interface in KDE for flatpak permissions per application. When I give Zen rw on all user files, it indeed creates a new .zen folder and a new profile, instead of using the one stored in the flatpak cache folder, but the crash and the warnings from Thunderbird remain unchanged.

The issue might be more likely to be found in Thunderbird. Just strange that it can launch Firefox without issue.