This is driving me nuts (and doesn't help that I've got a three-year-old tugging at my arm).
I've absolutely positioned this search form, but am having a pixel issue in FF 4. For illustrative purposes, I've colored the container red and positioned it top:0, right:3.
On the left, FF4. On the right, Chrome 10.
To make matters even more confusing, The border lines up properly when using the browser zoom:
There are no margins or padding. Firebug and Chrome's inspector reveal nothing.