User Agent: Mozilla/5.0 (Windows NT 6.0; rv:22.0) Gecko/20130312 Firefox/22.0 Build ID: 20130312031046 Steps to reproduce: 1. Browse to this attachment from another bug: https://bug836233.bugzilla.mozilla.org/attachment.cgi?id=719063 This image has multiple "widths", and where there is no background, firefox chooses to fill this area will grey. 2. Check the grey color on the top right of the attachment. Now download the image and view it on your desktop, you will notice the differences.
The background for transparent images in image documents was changed by Bug 793366. The grayish color is intentional.
Thank you for filing this bug. This change was intentional and it's not something we are planning on changing any time in the near future. This same problem existed with the previous implementation (image placed on top of a white background). In the previous implementation, it would have been hard for a user to know if the white area surrounding the image was part of the image or not, so the change in bug 793366 and bug 376997 did not regress this expectation.