In particular, restarting snapd doesn't help at all for me, so having the directory mounted before snapd starts doesn't help, and the same problem occurs with other file systems. However _starting_ outside the home directory does help. This is the situation for me with Kerberos authenticated NFS, and others with sshfs. I don't know whether it is relevant for people using NFS without authentication. It is easy to test for yourself - restart snapd and see if that helps.
So I think there is progress in understanding the problem, even if not working out how to fix it.
FYI: I initially tried a work around where I used the debian repository for firefox instead of the snap version, but despite giving it a higher priority (confirmed via "sudo apt policy firefox") I found the debian package twice over a week uninstalled and replaced by the snap version that then would not start. I can manually revert it but it is inconvenient. Any suggestions on how to make that work reliably would be appreciated.
Matthieu, more recently a more likely problem has been characterized by Alberto Mardegan and found the line in question in /bugs.launchpad .net/snapd/ +bug/1973321
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In particular, restarting snapd doesn't help at all for me, so having the directory mounted before snapd starts doesn't help, and the same problem occurs with other file systems. However _starting_ outside the home directory does help. This is the situation for me with Kerberos authenticated NFS, and others with sshfs. I don't know whether it is relevant for people using NFS without authentication. It is easy to test for yourself - restart snapd and see if that helps.
So I think there is progress in understanding the problem, even if not working out how to fix it.
FYI: I initially tried a work around where I used the debian repository for firefox instead of the snap version, but despite giving it a higher priority (confirmed via "sudo apt policy firefox") I found the debian package twice over a week uninstalled and replaced by the snap version that then would not start. I can manually revert it but it is inconvenient. Any suggestions on how to make that work reliably would be appreciated.