prevent font duplicates

Former-commit-id: 5e65b27810bde9781692ee2e5f617465bbf73c6e

lib/single-file/processors/hooks/content/content-hooks-frames.js

@@ -59,7 +59,12 @@ this.singlefile.lib.processors.hooks.content.frames = this.singlefile.lib.proces
 		scriptElement = document.createElement("script");
 		scriptElement.textContent = "(" + injectedScript.toString() + ")()";
 		(document.documentElement || document).appendChild(scriptElement);
-		addEventListener.call(window, NEW_FONT_FACE_EVENT, event => fontFaces.push(event.detail));
+		addEventListener.call(window, NEW_FONT_FACE_EVENT, event => {
+			const detail = event.detail;
+			if (!fontFaces.find(fontFace => JSON.stringify(fontFace) == JSON.stringify(detail))) {
+				fontFaces.push(event.detail);
+			}
+		});
 	}
 
 	return {