tampering with code and data on the workstation

[rvj]

I am pretty much a novice at security and therefore get the impression much
of the security issues are to do with transfer to and from host.

What mechanisms exist on the workstation to verify that downloaded code,
packages, etc are not subsequently tampered with.

Does Mozilla have any mechanism for verification checking on startup? e.g.
some sort of hash fingerprint maintained via the download or installation
routine