Interesting. It might just be a Firefox thing.

I remember reading a Firefox bug report about this, and the response was that the person's monitor colour calibration must be wrong, which makes no sense to me since even if the monitor colour calibration was wrong, I'd except it to apply to both the page and the image equally.

EDIT: This one: https://bugzilla.mozilla.org/show_bug.cgi?id=621474 - from 12 years ago.