Just to put my 2 cents..   Firefox has a bug report someone submitted .. but it is really not a bug it is what the SVG spec dictates, that when you try to access an element that is an SVG element that is either missing, has display:none or not visible. It will throw that NS_ERROR_FAILURE, since any element that is missing, has display:none or hidden will be removed from the render tree making it throw that error since it does not exist.   https://bugzilla.mozilla.org/show_bug.cgi?id=612118
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