don't map unknown font properties

lib/hooks/hooks-frame.js

@@ -62,7 +62,11 @@ this.hooksFrame = this.hooksFrame || (() => {
 				detail.src = argumentsList[1];
 				const descriptors = argumentsList[2];
 				if (descriptors) {
-					Object.keys(descriptors).forEach(descriptor => detail[FONT_STYLE_PROPERTIES[descriptor]] = descriptors[descriptor]);
+					Object.keys(descriptors).forEach(descriptor => {
+						if (FONT_STYLE_PROPERTIES[descriptor]) {
+							detail[FONT_STYLE_PROPERTIES[descriptor]] = descriptors[descriptor]
+						}
+					});
 				}
 				dispatchEvent(new CustomEvent(NEW_FONT_FACE_EVENT, { detail }));
 				return new FontFace(...argumentsList);