Just realized that targeted <animate> elements (which we've supported since bug 491080 in 2009) should probably be using nsReferencedElement::ResetWithId() (added in bug 474743 in 2010), instead of calling Reset() with a custom-created URI. As noted at http://www.w3.org/TR/SVG11/animate.html#HrefAttribute , "The target element must be part of the current SVG document fragment", which means ResetWithId() is a reasonable thing to use. (It assumes same-document.)