Query about browser security

Hi there -
I have noticed twice now that when I pull up my cached login credentials for Steemit, there is someone else's user name there.

I refresh and mine shows up. Has my browser been hacked? Haven't been using my usual shutdown procedures the last week or so. I drive a MacBook Pro which is, yes, a bit outdated and needs replacing this year but... are the warnings to use MacAfee or something like for MAC a good idea?

Rookie weirdness, I'm aware. Thoughts?