If you mean the boxes on the login page BEFORE logging in:
Just override what it fills the boxes in with.
It did it to me, and filled in an email I've never used on this site, but that has been used on other sites on this laptop. It's the browser that fills in those boxes.
Another thing this site does is; it fills in my username into the email box, then keeps telling me I put the wrong login details in. So I have to double check everything.
If you mean AFTER logging in, then I don't know how to fix that sorry.
