Heartbeat is an internet mechanism within Firefox, the messages some from a secure Mozilla server, and that is the only server Firefox can receive Heartbeat messages from.

If you are worried about security, it's best to keep Firefox and your OS up to date, as must security breaches happen due to out of date software.

Anytime you want or need to check for upgrades, go to the website of the True Owner of the program in question. For example, to check out Firefox, go to https://www.mozilla.org {web link}

You provide an acceptable solution, but you didn't really answer my question, which is, in other words, "Can a scammer send a similar message?"

I did tell you, no, a scammer cannot send those messages. Only Mozilla can