diff --git a/ext/src/background/receiverSelector/ReceiverSelector.ts b/ext/src/background/ReceiverSelector.ts
similarity index 84%
rename from ext/src/background/receiverSelector/ReceiverSelector.ts
rename to ext/src/background/ReceiverSelector.ts
index 618986d..acc4ce2 100644
--- a/ext/src/background/receiverSelector/ReceiverSelector.ts
+++ b/ext/src/background/ReceiverSelector.ts
@@ -1,35 +1,45 @@
 "use strict";
 
-import logger from "../../lib/logger";
-import messaging, { Port, Message } from "../../messaging";
-import options from "../../lib/options";
-
-import { TypedEventTarget } from "../../lib/TypedEventTarget";
-import { ReceiverDevice } from "../../types";
-import { SessionRequest } from "../../cast/sdk/classes";
+import logger from "../lib/logger";
+import messaging, { Port, Message } from "../messaging";
+import options from "../lib/options";
 
+import { TypedEventTarget } from "../lib/TypedEventTarget";
+import { SessionRequest } from "../cast/sdk/classes";
 import {
-    ReceiverSelectionCast,
-    ReceiverSelectionStop,
+    ReceiverDevice,
+    ReceiverSelectionActionType,
     ReceiverSelectorMediaType
-} from "./index";
+} from "../types";
 
 const POPUP_URL = browser.runtime.getURL("ui/popup/index.html");
 
-export interface PageInfo {
+/** Info about sender page context. */
+export interface ReceiverSelectorPageInfo {
     url: string;
     tabId: number;
     frameId: number;
     sessionRequest?: SessionRequest;
 }
 
+export interface ReceiverSelectionCast {
+    actionType: ReceiverSelectionActionType.Cast;
+    receiverDevice: ReceiverDevice;
+    mediaType: ReceiverSelectorMediaType;
+    filePath?: string;
+}
+export interface ReceiverSelectionStop {
+    actionType: ReceiverSelectionActionType.Stop;
+    receiverDevice: ReceiverDevice;
+}
+export type ReceiverSelection = ReceiverSelectionCast | ReceiverSelectionStop;
+
 interface ReceiverSelectorEvents {
     selected: ReceiverSelectionCast;
     error: string;
     cancelled: void;
     stop: ReceiverSelectionStop;
 }
-
 /**
  * Manages the receiver selector popup window and communication with the
  * extension page hosted within.
@@ -38,7 +48,7 @@ export default class ReceiverSelector extends TypedEventTarget<ReceiverSelectorE
     /** Popup window ID. */
     private windowId?: number;
 
-    /** Message port to extension page within popup window. */
+    /** Message port to extension page. */
     private messagePort?: Port;
     private messagePortDisconnected?: boolean;
 
@@ -50,9 +60,7 @@ export default class ReceiverSelector extends TypedEventTarget<ReceiverSelectorE
     private wasReceiverSelected = false;
 
     private appId?: string;
-    private pageInfo?: PageInfo;
-
-    #isOpen = false;
+    private pageInfo?: ReceiverSelectorPageInfo;
 
     constructor() {
         super();
@@ -63,6 +71,7 @@ export default class ReceiverSelector extends TypedEventTarget<ReceiverSelectorE
         this.onWindowsFocusChanged = this.onWindowsFocusChanged.bind(this);
 
         browser.windows.onRemoved.addListener(this.onWindowsRemoved);
+        browser.windows.onFocusChanged.addListener(this.onWindowsFocusChanged);
 
         /**
          * Handle incoming message channel connection from popup
@@ -73,7 +82,7 @@ export default class ReceiverSelector extends TypedEventTarget<ReceiverSelectorE
 
     /** Is receiver selector window currently open. */
     get isOpen() {
-        return this.#isOpen;
+        return this.windowId !== undefined;
     }
 
     /**
@@ -84,7 +93,7 @@ export default class ReceiverSelector extends TypedEventTarget<ReceiverSelectorE
         defaultMediaType: ReceiverSelectorMediaType;
         availableMediaTypes: ReceiverSelectorMediaType;
         appId?: string;
-        pageInfo?: PageInfo;
+        pageInfo?: ReceiverSelectorPageInfo;
     }) {
         this.appId = opts.appId;
         this.pageInfo = opts.pageInfo;
@@ -139,15 +148,7 @@ export default class ReceiverSelector extends TypedEventTarget<ReceiverSelectorE
             ...popupSizePosition
         });
 
-        this.#isOpen = true;
         this.windowId = popup.id;
-
-        // Add focus listener
-        if (await options.get("receiverSelectorCloseIfFocusLost")) {
-            browser.windows.onFocusChanged.addListener(
-                this.onWindowsFocusChanged
-            );
-        }
     }
 
     /** Updates receiver devices displayed in the receiver selector. */
@@ -258,8 +259,6 @@ export default class ReceiverSelector extends TypedEventTarget<ReceiverSelectorE
             return;
         }
 
-        this.#isOpen = false;
-
         browser.windows.onRemoved.removeListener(this.onWindowsRemoved);
         browser.windows.onFocusChanged.removeListener(
             this.onWindowsFocusChanged
@@ -279,21 +278,18 @@ export default class ReceiverSelector extends TypedEventTarget<ReceiverSelectorE
     }
 
     /**
-     * Closes popup window if another browser window is brought
-     * into focus. Doesn't apply if no window is focused
-     * `WINDOW_ID_NONE` or if the popup window is re-focused.
+     * Closes popup window if another browser window is brought into
+     * focus. Doesn't apply if no window is focused `WINDOW_ID_NONE`
+     * or if the popup window is re-focused.
      */
-    private onWindowsFocusChanged(windowId: number) {
+    private async onWindowsFocusChanged(windowId: number) {
+        if (!this.windowId) return;
+
         if (
             windowId !== browser.windows.WINDOW_ID_NONE &&
             windowId !== this.windowId
         ) {
-            // Only run once
-            browser.windows.onFocusChanged.removeListener(
-                this.onWindowsFocusChanged
-            );
-
-            if (this.windowId) {
+            if (await options.get("receiverSelectorCloseIfFocusLost")) {
                 browser.windows.remove(this.windowId);
             }
         }
diff --git a/ext/src/background/background.ts b/ext/src/background/background.ts
index 866ac41..0e55754 100755
--- a/ext/src/background/background.ts
+++ b/ext/src/background/background.ts
@@ -5,9 +5,9 @@ import logger from "../lib/logger";
 import options from "../lib/options";
 import bridge, { BridgeInfo } from "../lib/bridge";
 
-import CastManager from "../cast/CastManager";
-import receiverDevices from "./receiverDevices";
-import ReceiverSelectorManager from "./receiverSelector/ReceiverSelectorManager";
+import castManager from "./castManager";
+import deviceManager from "./deviceManager";
+import selectorManager from "./selectorManager";
 
 import { initMenus } from "./menus";
 import { initWhitelist } from "./whitelist";
@@ -101,8 +101,8 @@ async function init() {
 
     await notifyBridgeCompat();
 
-    await receiverDevices.init();
-    await CastManager.init();
+    await deviceManager.init();
+    await castManager.init();
 
     await initMenus();
     await initWhitelist();
@@ -119,9 +119,9 @@ async function init() {
             return;
         }
 
-        const selection = await ReceiverSelectorManager.getSelection(tab.id);
+        const selection = await selectorManager.getSelection(tab.id);
         if (selection) {
-            CastManager.loadSender({
+            castManager.loadSender({
                 tabId: tab.id,
                 frameId: 0,
                 selection
diff --git a/ext/src/cast/CastManager.ts b/ext/src/background/castManager.ts
similarity index 92%
rename from ext/src/cast/CastManager.ts
rename to ext/src/background/castManager.ts
index db2b57d..6115b99 100644
--- a/ext/src/cast/CastManager.ts
+++ b/ext/src/background/castManager.ts
@@ -7,13 +7,14 @@ import options from "../lib/options";
 import { stringify } from "../lib/utils";
 
 import {
-    ReceiverSelection,
     ReceiverSelectionActionType,
     ReceiverSelectorMediaType
-} from "../background/receiverSelector";
+} from "../types";
 
-import ReceiverSelectorManager from "../background/receiverSelector/ReceiverSelectorManager";
-import receiverDevices from "../background/receiverDevices";
+import { ReceiverSelection } from "./ReceiverSelector";
+
+import deviceManager from "./deviceManager";
+import selectorManager from "./selectorManager";
 
 type AnyPort = Port | MessagePort;
 
@@ -26,7 +27,7 @@ export interface CastInstance {
 }
 
 /** Keeps track of cast API instances and provides bridge messaging. */
-export default new (class CastManager {
+export default new (class {
     private activeInstances = new Set<CastInstance>();
 
     public async init() {
@@ -38,7 +39,7 @@ export default new (class CastManager {
         });
 
         // Forward receiver eventes to cast instances
-        receiverDevices.addEventListener("receiverDeviceUp", ev => {
+        deviceManager.addEventListener("receiverDeviceUp", ev => {
             for (const instance of this.activeInstances) {
                 instance.contentPort.postMessage({
                     subject: "cast:receiverDeviceUp",
@@ -46,7 +47,7 @@ export default new (class CastManager {
                 });
             }
         });
-        receiverDevices.addEventListener("receiverDeviceDown", ev => {
+        deviceManager.addEventListener("receiverDeviceDown", ev => {
             for (const instance of this.activeInstances) {
                 instance.contentPort.postMessage({
                     subject: "cast:receiverDeviceDown",
@@ -202,7 +203,7 @@ export default new (class CastManager {
             case "main:initializeCast": {
                 instance.appId = message.data.appId;
 
-                for (const receiverDevice of receiverDevices.getDevices()) {
+                for (const receiverDevice of deviceManager.getDevices()) {
                     instance.contentPort.postMessage({
                         subject: "cast:receiverDeviceUp",
                         data: { receiverDevice }
@@ -224,12 +225,11 @@ export default new (class CastManager {
                 }
 
                 try {
-                    const selection =
-                        await ReceiverSelectorManager.getSelection(
-                            instance.contentTabId,
-                            instance.contentFrameId,
-                            { sessionRequest: message.data.sessionRequest }
-                        );
+                    const selection = await selectorManager.getSelection(
+                        instance.contentTabId,
+                        instance.contentFrameId,
+                        { sessionRequest: message.data.sessionRequest }
+                    );
 
                     // Handle cancellation
                     if (!selection) {
@@ -297,7 +297,7 @@ export default new (class CastManager {
              * same one that caused the session creation.
              */
             case "main:closeReceiverSelector": {
-                const selector = await ReceiverSelectorManager.getSelector();
+                const selector = await selectorManager.getSelector();
                 const shouldClose = await options.get(
                     "receiverSelectorWaitForConnection"
                 );
@@ -366,7 +366,7 @@ export default new (class CastManager {
 
             case ReceiverSelectorMediaType.File: {
                 const fileUrl = new URL(`file://${opts.selection.filePath}`);
-                const { init } = await import("./senders/media");
+                const { init } = await import("../cast/senders/media");
 
                 init({
                     mediaUrl: fileUrl.href,
diff --git a/ext/src/background/receiverDevices.ts b/ext/src/background/deviceManager.ts
similarity index 100%
rename from ext/src/background/receiverDevices.ts
rename to ext/src/background/deviceManager.ts
diff --git a/ext/src/background/menus.ts b/ext/src/background/menus.ts
index 960476b..eb0a37a 100644
--- a/ext/src/background/menus.ts
+++ b/ext/src/background/menus.ts
@@ -2,17 +2,17 @@
 
 import logger from "../lib/logger";
 import options from "../lib/options";
-
 import { stringify } from "../lib/utils";
 
 import {
-    ReceiverSelection,
     ReceiverSelectionActionType,
     ReceiverSelectorMediaType
-} from "./receiverSelector";
+} from "../types";
 
-import ReceiverSelectorManager from "./receiverSelector/ReceiverSelectorManager";
-import CastManager from "../cast/CastManager";
+import { ReceiverSelection } from "./ReceiverSelector";
+
+import selectorManager from "./selectorManager";
+import castManager from "./castManager";
 
 const _ = browser.i18n.getMessage;
 
@@ -142,7 +142,7 @@ async function onMenuClicked(
 
         let selection: Nullable<ReceiverSelection> = null;
         try {
-            selection = await ReceiverSelectorManager.getSelection(
+            selection = await selectorManager.getSelection(
                 tab.id,
                 info.frameId,
                 { withMediaSender: castMediaMenuClicked }
@@ -160,7 +160,7 @@ async function onMenuClicked(
         }
 
         if (castMenuClicked) {
-            CastManager.loadSender({
+            castManager.loadSender({
                 tabId: tab.id,
                 frameId: info.frameId,
                 selection
@@ -187,7 +187,7 @@ async function onMenuClicked(
                 });
             } else {
                 // Handle other responses
-                CastManager.loadSender({
+                castManager.loadSender({
                     tabId: tab.id,
                     frameId: info.frameId,
                     selection
diff --git a/ext/src/background/receiverSelector/index.ts b/ext/src/background/receiverSelector/index.ts
deleted file mode 100644
index 441377c..0000000
--- a/ext/src/background/receiverSelector/index.ts
+++ /dev/null
@@ -1,29 +0,0 @@
-"use strict";
-
-import { ReceiverDevice } from "../../types";
-
-export enum ReceiverSelectorMediaType {
-    None = 0,
-    App = 1,
-    Tab = 2,
-    Screen = 4,
-    File = 8
-}
-
-export enum ReceiverSelectionActionType {
-    Cast = 1,
-    Stop = 2
-}
-
-export interface ReceiverSelectionCast {
-    actionType: ReceiverSelectionActionType.Cast;
-    receiverDevice: ReceiverDevice;
-    mediaType: ReceiverSelectorMediaType;
-    filePath?: string;
-}
-export interface ReceiverSelectionStop {
-    actionType: ReceiverSelectionActionType.Stop;
-    receiverDevice: ReceiverDevice;
-}
-
-export type ReceiverSelection = ReceiverSelectionCast | ReceiverSelectionStop;
diff --git a/ext/src/background/receiverSelector/ReceiverSelectorManager.ts b/ext/src/background/selectorManager.ts
similarity index 83%
rename from ext/src/background/receiverSelector/ReceiverSelectorManager.ts
rename to ext/src/background/selectorManager.ts
index dde986f..25b001d 100644
--- a/ext/src/background/receiverSelector/ReceiverSelectorManager.ts
+++ b/ext/src/background/selectorManager.ts
@@ -1,23 +1,24 @@
 "use strict";
 
-import options from "../../lib/options";
-import logger from "../../lib/logger";
+import options from "../lib/options";
+import logger from "../lib/logger";
 
-import CastManager from "../../cast/CastManager";
-import { SessionRequest } from "../../cast/sdk/classes";
-import receiverDevices from "../receiverDevices";
+import { getMediaTypesForPageUrl } from "../lib/utils";
+import { SessionRequest } from "../cast/sdk/classes";
 
-import { getMediaTypesForPageUrl } from "../../lib/utils";
+import castManager from "./castManager";
+import deviceManager from "./deviceManager";
+
+import ReceiverSelector, {
+    ReceiverSelection,
+    ReceiverSelectionCast,
+    ReceiverSelectionStop
+} from "./ReceiverSelector";
 
 import {
-    ReceiverSelection,
     ReceiverSelectionActionType,
-    ReceiverSelectionCast,
-    ReceiverSelectionStop,
     ReceiverSelectorMediaType
-} from "./index";
-
-import ReceiverSelector from "./ReceiverSelector";
+} from "../types";
 
 let sharedSelector: ReceiverSelector;
 async function getSelector() {
@@ -46,12 +47,12 @@ async function getSelection(
     contextTabId: number,
     contextFrameId = 0,
     selectionOpts?: {
-        sessionRequest: SessionRequest;
+        sessionRequest?: SessionRequest;
         withMediaSender?: boolean;
     }
 ): Promise<ReceiverSelection | null> {
     return new Promise(async (resolve, reject) => {
-        let castInstance = CastManager.getInstance(
+        let castInstance = castManager.getInstance(
             contextTabId,
             contextFrameId
         );
@@ -112,15 +113,12 @@ async function getSelection(
         sharedSelector = new ReceiverSelector();
 
         function onReceiverChange() {
-            sharedSelector.update(receiverDevices.getDevices());
+            sharedSelector.update(deviceManager.getDevices());
         }
 
-        receiverDevices.addEventListener("receiverDeviceUp", onReceiverChange);
-        receiverDevices.addEventListener(
-            "receiverDeviceDown",
-            onReceiverChange
-        );
-        receiverDevices.addEventListener(
+        deviceManager.addEventListener("receiverDeviceUp", onReceiverChange);
+        deviceManager.addEventListener("receiverDeviceDown", onReceiverChange);
+        deviceManager.addEventListener(
             "receiverDeviceUpdated",
             onReceiverChange
         );
@@ -139,7 +137,7 @@ async function getSelection(
         function onSelectorStop(ev: CustomEvent<ReceiverSelectionStop>) {
             logger.info("Stopping receiver app...", ev.detail);
 
-            receiverDevices.stopReceiverApp(ev.detail.receiverDevice.id);
+            deviceManager.stopReceiverApp(ev.detail.receiverDevice.id);
 
             removeListeners();
             resolve({
@@ -172,25 +170,25 @@ async function getSelection(
             );
             sharedSelector.removeEventListener("error", onSelectorError);
 
-            receiverDevices.removeEventListener(
+            deviceManager.removeEventListener(
                 "receiverDeviceUp",
                 onReceiverChange
             );
-            receiverDevices.removeEventListener(
+            deviceManager.removeEventListener(
                 "receiverDeviceDown",
                 onReceiverChange
             );
-            receiverDevices.removeEventListener(
+            deviceManager.removeEventListener(
                 "receiverDeviceUpdated",
                 onReceiverChange
             );
         }
 
         // Ensure status manager is initialized
-        await receiverDevices.init();
+        await deviceManager.init();
 
         sharedSelector.open({
-            receiverDevices: receiverDevices.getDevices(),
+            receiverDevices: deviceManager.getDevices(),
             defaultMediaType,
             availableMediaTypes,
             appId: castInstance?.appId,
diff --git a/ext/src/cast/content.ts b/ext/src/cast/content.ts
index 650bc99..98b2110 100644
--- a/ext/src/cast/content.ts
+++ b/ext/src/cast/content.ts
@@ -32,7 +32,7 @@ Reflect.defineProperty(HTMLScriptElement.prototype.wrappedJSObject, "src", {
     enumerable: true,
     get: desc?.get,
 
-    set: exportFunction(function setFunc(this: HTMLScriptElement, value) {
+    set: exportFunction(function (this: HTMLScriptElement, value: string) {
         if (CAST_SCRIPT_URLS.includes(value)) {
             return desc?.set?.call(this, CAST_LOADER_SCRIPT_URL);
         }
diff --git a/ext/src/cast/export.ts b/ext/src/cast/export.ts
index 171f1ea..c5895cc 100644
--- a/ext/src/cast/export.ts
+++ b/ext/src/cast/export.ts
@@ -48,11 +48,13 @@ export function ensureInit(): Promise<TypedMessagePort<Message>> {
          * URL.
          */
         if (window.location.protocol === "moz-extension:") {
-            const { default: CastManager } = await import("./CastManager");
+            const { default: castManager } = await import(
+                "../background/castManager"
+            );
 
             // port2 will post bridge messages to port 1
-            await CastManager.init();
-            await CastManager.createInstance(channel.port2);
+            await castManager.init();
+            await castManager.createInstance(channel.port2);
 
             // bridge -> cast instance
             channel.port1.onmessage = ev => {
diff --git a/ext/src/cast/sdk/index.ts b/ext/src/cast/sdk/index.ts
index 803ac3d..478634d 100644
--- a/ext/src/cast/sdk/index.ts
+++ b/ext/src/cast/sdk/index.ts
@@ -2,10 +2,7 @@
 
 import logger from "../../lib/logger";
 
-import {
-    ReceiverDevice,
-    ReceiverDeviceCapabilities as ReceiverDeviceCapabilities
-} from "../../types";
+import { ReceiverDevice, ReceiverDeviceCapabilities } from "../../types";
 import { ErrorCallback, SuccessCallback } from "../types";
 
 import eventMessaging from "../eventMessaging";
diff --git a/ext/src/cast/senders/mirroring.ts b/ext/src/cast/senders/mirroring.ts
index 23cf3b1..a9f2e23 100644
--- a/ext/src/cast/senders/mirroring.ts
+++ b/ext/src/cast/senders/mirroring.ts
@@ -3,8 +3,7 @@
 import options from "../../lib/options";
 import cast, { ensureInit } from "../export";
 
-import { ReceiverSelectorMediaType } from "../../background/receiverSelector";
-import { ReceiverDevice } from "../../types";
+import { ReceiverDevice, ReceiverSelectorMediaType } from "../../types";
 
 import type Session from "../sdk/Session";
 
diff --git a/ext/src/lib/utils.ts b/ext/src/lib/utils.ts
index 39c3993..0cfde5d 100644
--- a/ext/src/lib/utils.ts
+++ b/ext/src/lib/utils.ts
@@ -1,6 +1,6 @@
 "use strict";
 
-import { ReceiverSelectorMediaType } from "../background/receiverSelector";
+import { ReceiverSelectorMediaType } from "../types";
 
 export function getNextEllipsis(ellipsis: string): string {
     if (ellipsis === "") return ".";
diff --git a/ext/src/messaging.ts b/ext/src/messaging.ts
index 66c5ada..7429b12 100644
--- a/ext/src/messaging.ts
+++ b/ext/src/messaging.ts
@@ -3,7 +3,6 @@
 import { TypedPort } from "./lib/TypedPort";
 import { BridgeInfo } from "./lib/bridge";
 
-import { ReceiverSelectorMediaType } from "./background/receiverSelector";
 import {
     ReceiverSelection,
     ReceiverSelectionCast,
@@ -19,7 +18,7 @@ import {
 } from "./cast/sdk/types";
 import { SessionRequest } from "./cast/sdk/classes";
 
-import { ReceiverDevice } from "./types";
+import { ReceiverDevice, ReceiverSelectorMediaType } from "./types";
 
 /**
  * Messages are JSON objects with a `subject` string key and a
diff --git a/ext/src/types.ts b/ext/src/types.ts
index f4f4d01..21695fa 100644
--- a/ext/src/types.ts
+++ b/ext/src/types.ts
@@ -20,3 +20,15 @@ export interface ReceiverDevice {
     port: number;
     status?: ReceiverStatus;
 }
+
+export enum ReceiverSelectorMediaType {
+    None = 0,
+    App = 1,
+    Tab = 2,
+    Screen = 4,
+    File = 8
+}
+export enum ReceiverSelectionActionType {
+    Cast = 1,
+    Stop = 2
+}
diff --git a/ext/src/ui/popup/index.tsx b/ext/src/ui/popup/index.tsx
index 0a5f324..cc1dc7b 100755
--- a/ext/src/ui/popup/index.tsx
+++ b/ext/src/ui/popup/index.tsx
@@ -11,14 +11,15 @@ import messaging, { Message, Port } from "../../messaging";
 import { getNextEllipsis } from "../../lib/utils";
 import { RemoteMatchPattern } from "../../lib/matchPattern";
 
-import { ReceiverDevice, ReceiverDeviceCapabilities } from "../../types";
-import { Capability } from "../../cast/sdk/enums";
-
 import {
+    ReceiverDevice,
+    ReceiverDeviceCapabilities,
     ReceiverSelectionActionType,
     ReceiverSelectorMediaType
-} from "../../background/receiverSelector";
-import { PageInfo } from "../../background/receiverSelector/ReceiverSelector";
+} from "../../types";
+
+import { ReceiverSelectorPageInfo } from "../../background/ReceiverSelector";
+import { Capability } from "../../cast/sdk/enums";
 
 const _ = browser.i18n.getMessage;
 
@@ -73,7 +74,7 @@ interface PopupAppState {
 
     filePath?: string;
     appId?: string;
-    pageInfo?: PageInfo;
+    pageInfo?: ReceiverSelectorPageInfo;
 
     mirroringEnabled: boolean;
     userAgentWhitelistEnabled: boolean;
@@ -405,7 +406,10 @@ class PopupApp extends Component<PopupAppProps, PopupAppState> {
         );
     }
 
-    private async onAddToWhitelist(app: KnownApp, pageInfo: PageInfo) {
+    private async onAddToWhitelist(
+        app: KnownApp,
+        pageInfo: ReceiverSelectorPageInfo
+    ) {
         if (!app.matches) {
             return;
         }