User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US; rv:1.9.0.3) Gecko/2008092414 Firefox/3.0.3 Build Identifier: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; en-US; rv:1.9.0.3) Gecko/2008092414 Firefox/3.0.3 As you can see in the example, the background image position is centered. It seems to be true, but the background image is placed 1px to the right from the center. You can see it on the left side of top navigation, where is 1px width line. Watch carefully, it's only a detail. Just try the same example on other web-browsers (Internet Explorer, Opera, Safari or older versions of Firefox, etc.) - there is no line, so the background image is really in the center. I've found this issue also on other webpages Reproducible: Always Steps to Reproduce: 1. 2. 3.

Yes, this bug is similar to bug 446284, but in my example you can see it even the browser is not resized.

Depending on the (pixel-) size of your window :-) An even or odd number will work fine. I had to resize the indow on my side to see the issue.