This is a demo HTML file showing a rendering bug in Firefox.

The outer div element has its background set to an image: centered and tiled vertically.

The inner div element has width set to 748 pixels and left and right margins set to auto, which basically means, the div contents are centered. The whole div area should be black.

The size of the inner div is exactly the size of white space in the image minus 2 pixel. This renders as two 1 pixel wide bars outside the black area.

Unfortunately when the outer div element is odd-number wide, the image is moved one pixel left from the inner div element, which renders as a single 2 pixel wide bar at the left of the black area and nothing at the right

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