Convert SVG's to PNGs. This works OK if the SVG's styles are inline. The SVG element must contain an xmlns attribute. Webkit also requires you specify a font size on `text` elements.

svg-to-png.js

var svg  = document.getElementById('graph'),
    xml  = new XMLSerializer().serializeToString(svg),
    data = "data:image/svg+xml;base64," + btoa(xml),
    img  = new Image()

img.setAttribute('src', data)
document.body.appendChild(img)

I'm trying to doit with a Highmaps svg but it throws InvalidCharacterError: String contains an invalid character

This does NOT convert SVG images to PNG. In fact, it does not transform the data at all, all it does is take an SVG element in the document tree, serialize it as text, create a data URI with the text embedded, and create an image that uses said URI, in effect creating an image with the entire image source embedded in the URI. PNG does not figure into this at all.

Nice, worked perfectly to make an embedded SVG downloadable!