In any given JS context, if one creates a FontFace object by: new FontFace("MyFont2", "url(\"asdf\")", {}). The url attribute of the object will not be resolved correctly if a relative URL is given as the base URL will be interpreted as empty URL.
<rdar://problem/25638820>
See issue 5 in the spec: "Need to define the base url, so relative urls can resolve. Should it be the url of the document? Is that correct for workers too, or should they use their worker url? Is that always defined?" I can't fix this in WebKit until the spec describes the correct behavior.