Comment 97 for bug 168261

To add to my comment above, it seems this also affects setting SVGs as CSS background images as they behave in a slightly similar way to object (displaying the image actual size rather than resizing to fit the bounding box) - testing in Opera this is particularly apparent when zooming a page with SVG CSS background images lacking viewBox.

Adding the viewBox attribute does seem to suit the use of SVGs in CSS a lot more than the fixed height and width does as far as I can tell.