remove initResponse listener once called

lib/frame-tree/bg/frame-tree.js

@@ -34,11 +34,13 @@ this.FrameTree = (() => {
 	return {
 		async initialize(tabId) {
 			return new Promise(resolve => {
-				browser.runtime.onMessage.addListener(message => {
+				const onMessage = message => {
 					if (message.method == "FrameTree.initResponse") {
+						browser.runtime.onMessage.removeListener(onMessage);
 						resolve();
 					}
-				});
+				};
+				browser.runtime.onMessage.addListener(onMessage);
 				browser.tabs.sendMessage(tabId, { method: "FrameTree.initRequest", windowId: "0", index: 0 });
 			});
 		}