Generate the MD5 hash of any text, for checksums and cache keys.
MD5 is fine for checksums and cache keys but is broken for security. Don't use it for passwords or signatures.
No. It is broken for security use but fine for quick checksums.
Not directly, but short or common inputs can be looked up, so never use it for passwords.
No. Everything is worked out in your browser and nothing you type is sent to a server.