I haven’t ever used Firejail, but I know a little about it. I understand that Firejail depends on you configuring things for each app, with a mixture of whitelisting and blacklisting. That’s untenable unless the default profile is safe. You said its default profile just makes the home directory read-only; I took that at face value (since I have no interest in installing it to check). If what you said was correct, then I presume that either you must have changed the default profile, or Bash is using a different profile?