SVG files that take up an area larger than the browser content area should scroll, but the change to svg.css in the patch for bug 769645 has broken that. The reason for that change was to prevent SVGs that are smaller than the viewport from painting outside their content area (needed for backwards compatibility), but I think the value that we really need is 'scroll', not 'hidden'. I need to run some tests to check that both fixes this bug and keeps us backwards compatible, but if it works I'll attach a patch.
in svg.css doesn't work since it causes SVG files embedded using <embed> to get scrollbars when they didn't previously. For example, the references for the following two tests are given scrollbars when they should not be:
Created attachment 640102 [details] [diff] [review]
Let's just go back to clipping without checking IsScrollableOverflow(), as we used to, but still using the nsDisplayClip to do the clipping. Right now I don't have any more time to spend on this, so I'll look into giving users more clipping control in bug 378923 later.