Yeah, seems highly unlikely to ever yield any results. Even if you did manage to read a file, you have to get lucky finding a password hash in a rainbow table or the password being shit enough to crack.

Holy shit this is kind of unsettling. Though I would expect ALL major browsers to reject reading any local files like this..... would this kind of thing actually succeed somewhere/somehow?

Before I even clicked the link, I was hoping it would lead to Ben Eater's video! I've gone through many tutorials/guides/videos on the subject of USB, and this video is the only one which really broke it down and presented it in a comprehensible manner.

I highly recommend all of his content if you are interested in electronics at all.