As others have suggested this is a snap app issue with /tmp dirs and can be verified with:
gnome-software --local-filename '/tmp/mozilla_user0/app_amd64.deb'
snap-store --local-filename '/tmp/mozilla_user0/app_amd64.deb'
I have added workaround to AU to use 'gnome-software' for opening debs: https://askubuntu.com/a/1330582/8570
I did also find an alterntive workaround so that all snap apps have access to /tmp: https://askubuntu.com/a/1264341/8570
As others have suggested this is a snap app issue with /tmp dirs and can be verified with:
gnome-software --local-filename '/tmp/mozilla_ user0/app_ amd64.deb'
snap-store --local-filename '/tmp/mozilla_ user0/app_ amd64.deb'
I have added workaround to AU to use 'gnome-software' for opening debs: https:/ /askubuntu. com/a/1330582/ 8570
I did also find an alterntive workaround so that all snap apps have access to /tmp: https:/ /askubuntu. com/a/1264341/ 8570