Fedora Thunderbird flatpak crashes attaching or saving a file

The latest flatpak version of Thunderbird from Fedora (not Flathub):

Commit: 936d9f60ac420057270d5c0c26b3383b04177b678afd6f6e7b7b59df3f0e6663
Subject: Export net.thunderbird.Thunderbird
Date: 2025-10-12 19:21:33 +0000

Crashes when trying to attach a file or save an attachment:

[Parent 3, Main Thread] WARNING: Could not load a pixbuf from icon theme.
This may indicate that pixbuf loaders or the mime database could not be found.: 'glib warning', file /builddir/build/BUILD/thunderbird-140.3.0-build/thunderbird-140.3.0/toolkit/xre/nsSigHandlers.cpp:201

(net.thunderbird.Thunderbird:3): Gtk-WARNING **: 12:25:17.580: Could not load a pixbuf from icon theme.
This may indicate that pixbuf loaders or the mime database could not be found.
**
Gtk:ERROR:../gtk/gtkiconhelper.c:495:ensure_surface_for_gicon: assertion failed (error == NULL): Failed to load /run/host/share/icons/breeze/status/16/image-missing.svg: Failed to create file “~/.var/app/net.thunderbird.Thunderbird/cache/tmp/gdk-pixbuf-glycin-tmp.KSAZE3”: No such file or directory (g-file-error-quark, 4)
Bail out! Gtk:ERROR:../gtk/gtkiconhelper.c:495:ensure_surface_for_gicon: assertion failed (error == NULL): Failed to load /run/host/share/icons/breeze/status/16/image-missing.svg: Failed to create file “~/.var/app/net.thunderbird.Thunderbird/cache/tmp/gdk-pixbuf-glycin-tmp.KSAZE3”: No such file or directory (g-file-error-quark, 4)
Redirecting call to abort() to mozalloc_abort

Exiting due to channel error.
Segmentation fault         (core dumped) thunderbird
[📦 net.thunderbird.Thunderbird ~]$ exit
exit

There is already a Bugzilla entry but until it is solved you can simply remove the TMPDIR environment variable:

flatpak override --user --unset-env=TMPDIR net.thunderbird.Thunderbird

To check that it has been done:

cat ~/.local/share/flatpak/overrides/net.thunderbird.Thunderbird
[Environment]
TMPDIR=

[Context]
unset-environment=TMPDIR; 

Now just run Thunderbird as usual and it will again allow to save and attach files.

To later remove the override once Fedora has fixed the bug just run:

flatpak override --user --unset-env=TMPDIR net.thunderbird.Thunderbird