Recently, I have downloaded a bit of adwatre hidden in free programs and noticed that the mail text box (at the bottom of the page) turned yellow along with other text boxes. I immediately did a virus and spyware scan and deleted everything found.
Astonished the problem was still there, I did adjusted by browser settings individually and found the culprit itself was the trusty Auto-Fill function on the Google Toolbar.
Has anyone else had this problem or was it a misinstallation?