Firejail does not restrict access to --tmpfs, which allows local users to gain privileges, as demonstrated by mounting over /etc.
{ "availability": "No subscription required", "binaries": [ { "binary_version": "0.9.38-1", "binary_name": "firejail" }, { "binary_version": "0.9.38-1", "binary_name": "firejail-dbgsym" } ] }