Ah ! Là, si c'est pas Firefox qui bug, je m'appelle plus Anne-Marie (comme dirait ma belle mère) :
z3@z3:~$ firefox --profilemanager
###!!! [Child][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
(/usr/lib/firefox/firefox:15060): dconf-WARNING **: 14:13:01.119: Unable to open /var/lib/flatpak/exports/share/dconf/profile/user: Permission non accordée
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
[Child 11949, MediaDecoderStateMachine #2] WARNING: Decoder=7f3ae56dbc00 Decode error: NS_ERROR_DOM_MEDIA_FATAL_ERR (0x806e0005) - RefPtr<MediaSourceTrackDemuxer::SamplesPromise> mozilla::MediaSourceTrackDemuxer::DoGetSamples(int32_t): manager is detached.: file /build/firefox-Dwa0M7/firefox-84.0+build3/dom/media/MediaDecoderStateMachine.cpp:3471
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
###!!! [Parent][RunMessage] Error: Channel closing: too late to send/recv, messages will be lost
IPDL protocol error: Handler returned error code!
###!!! [Parent][DispatchAsyncMessage] Error: PMessagePort::Msg_PostMessages Processing error: message was deserialized, but the handler returned false (indicating failure)
Exiting due to channel error.
Exiting due to channel error.
Exiting due to channel error.
Exiting due to channel error.
Exiting due to channel error.
Exiting due to channel error.
Processus arrêté
z3@z3:~$
Visiblement, en lisant là :
https://forum.ubuntu-fr.org/viewtopic.php?id=2044161&p=2 ça pourrait venir de la version "Flatpak" de Firefox. Je vias tenter de l'installer différemment.