replaced unneeded === with ==

extension/core/content/content.js

@@ -28,7 +28,7 @@ this.singlefile.top = this.singlefile.top || (() => {
 		return {};
 	});
 	addEventListener("message", event => {
-		if (typeof event.data === "string" && event.data.startsWith("__SingleFile__::")) {
+		if (typeof event.data == "string" && event.data.startsWith("__SingleFile__::")) {
 			const message = JSON.parse(event.data.substring("__SingleFile__".length + 2));
 			savePage(message);
 		}

lib/frame-tree/content/frame-tree.js

@@ -55,7 +55,7 @@ this.FrameTree = this.FrameTree || (() => {
 		}
 	});
 	addEventListener("message", event => {
-		if (typeof event.data === "string" && event.data.startsWith(MESSAGE_PREFIX + "::")) {
+		if (typeof event.data == "string" && event.data.startsWith(MESSAGE_PREFIX + "::")) {
 			const message = JSON.parse(event.data.substring(MESSAGE_PREFIX.length + 2));
 			if (message.method == "initRequest") {
 				initRequest(message);
@@ -154,7 +154,7 @@ this.FrameTree = this.FrameTree || (() => {
 			}
 
 			function onMessage(event) {
-				if (typeof event.data === "string" && event.data.startsWith(MESSAGE_PREFIX + "::")) {
+				if (typeof event.data == "string" && event.data.startsWith(MESSAGE_PREFIX + "::")) {
 					const message = JSON.parse(event.data.substring(MESSAGE_PREFIX.length + 2));
 					if (message.method == "getDataRequest" && message.windowId == frameWinId) {
 						topWindow.removeEventListener("message", onMessage, false);