diff --git a/toolkit/components/extensions/Extension.jsm b/toolkit/components/extensions/Extension.jsm
index 2a4abd92af6..2733f07b4b3 100644
--- a/toolkit/components/extensions/Extension.jsm
+++ b/toolkit/components/extensions/Extension.jsm
@@ -81,6 +81,7 @@ ExtensionManagement.registerSchema("chrome://extensions/content/schemas/web_requ
 
 Cu.import("resource://gre/modules/ExtensionUtils.jsm");
 var {
+  BaseContext,
   LocaleData,
   MessageBroker,
   Messenger,
@@ -218,63 +219,45 @@ var gContextId = 0;
 // |uri| is the URI of the content (optional).
 // |docShell| is the docshell the content runs in (optional).
 // |incognito| is the content running in a private context (default: false).
-ExtensionPage = function(extension, params) {
-  let {type, contentWindow, uri} = params;
-  this.extension = extension;
-  this.type = type;
-  this.contentWindow = contentWindow || null;
-  this.uri = uri || extension.baseURI;
-  this.incognito = params.incognito || false;
-  this.onClose = new Set();
-  this.contextId = gContextId++;
-  this.unloaded = false;
+ExtensionPage = class extends BaseContext {
+  constructor(extension, params) {
+    super();
 
-  // This is the MessageSender property passed to extension.
-  // It can be augmented by the "page-open" hook.
-  let sender = {id: extension.uuid};
-  if (uri) {
-    sender.url = uri.spec;
+    let {type, contentWindow, uri} = params;
+    this.extension = extension;
+    this.type = type;
+    this.contentWindow = contentWindow || null;
+    this.uri = uri || extension.baseURI;
+    this.incognito = params.incognito || false;
+    this.contextId = gContextId++;
+    this.unloaded = false;
+
+    // This is the MessageSender property passed to extension.
+    // It can be augmented by the "page-open" hook.
+    let sender = {id: extension.uuid};
+    if (uri) {
+      sender.url = uri.spec;
+    }
+    let delegate = {
+      getSender() {},
+    };
+    Management.emit("page-load", this, params, sender, delegate);
+
+    // Properties in |filter| must match those in the |recipient|
+    // parameter of sendMessage.
+    let filter = {extensionId: extension.id};
+    this.messenger = new Messenger(this, globalBroker, sender, filter, delegate);
+
+    this.extension.views.add(this);
   }
-  let delegate = {
-    getSender() {},
-  };
-  Management.emit("page-load", this, params, sender, delegate);
 
-  // Properties in |filter| must match those in the |recipient|
-  // parameter of sendMessage.
-  let filter = {extensionId: extension.id};
-  this.messenger = new Messenger(this, globalBroker, sender, filter, delegate);
-
-  this.extension.views.add(this);
-};
-
-ExtensionPage.prototype = {
   get cloneScope() {
     return this.contentWindow;
-  },
+  }
 
   get principal() {
     return this.contentWindow.document.nodePrincipal;
-  },
-
-  checkLoadURL(url, options = {}) {
-    let ssm = Services.scriptSecurityManager;
-
-    let flags = ssm.STANDARD;
-    if (!options.allowScript) {
-      flags |= ssm.DISALLOW_SCRIPT;
-    }
-    if (!options.allowInheritsPrincipal) {
-      flags |= ssm.DISALLOW_INHERIT_PRINCIPAL;
-    }
-
-    try {
-      ssm.checkLoadURIStrWithPrincipal(this.principal, url, flags);
-    } catch (e) {
-      return false;
-    }
-    return true;
-  },
+  }
 
   // A wrapper around MessageChannel.sendMessage which adds the extension ID
   // to the recipient object, and ensures replies are not processed after the
@@ -285,21 +268,13 @@ ExtensionPage.prototype = {
     sender.contextId = this.contextId;
 
     return MessageChannel.sendMessage(target, messageName, data, recipient, sender);
-  },
-
-  callOnClose(obj) {
-    this.onClose.add(obj);
-  },
-
-  forgetOnClose(obj) {
-    this.onClose.delete(obj);
-  },
+  }
 
   // Called when the extension shuts down.
   shutdown() {
     Management.emit("page-shutdown", this);
     this.unload();
-  },
+  }
 
   // This method is called when an extension page navigates away or
   // its tab is closed.
@@ -322,10 +297,8 @@ ExtensionPage.prototype = {
 
     this.extension.views.delete(this);
 
-    for (let obj of this.onClose) {
-      obj.close();
-    }
-  },
+    super.unload();
+  }
 };
 
 // Responsible for loading extension APIs into the right globals.
diff --git a/toolkit/components/extensions/ExtensionContent.jsm b/toolkit/components/extensions/ExtensionContent.jsm
index 96f9fb51258..13e64e08f23 100644
--- a/toolkit/components/extensions/ExtensionContent.jsm
+++ b/toolkit/components/extensions/ExtensionContent.jsm
@@ -37,6 +37,7 @@ XPCOMUtils.defineLazyModuleGetter(this, "MessageChannel",
 Cu.import("resource://gre/modules/ExtensionUtils.jsm");
 var {
   runSafeSyncWithoutClone,
+  BaseContext,
   LocaleData,
   MessageBroker,
   Messenger,
@@ -227,109 +228,103 @@ var ExtensionManager;
 // Scope in which extension content script code can run. It uses
 // Cu.Sandbox to run the code. There is a separate scope for each
 // frame.
-function ExtensionContext(extensionId, contentWindow, contextOptions = {}) {
-  let { isExtensionPage } = contextOptions;
+class ExtensionContext extends BaseContext {
+  constructor(extensionId, contentWindow, contextOptions = {}) {
+    super();
 
-  this.isExtensionPage = isExtensionPage;
-  this.extension = ExtensionManager.get(extensionId);
-  this.extensionId = extensionId;
-  this.contentWindow = contentWindow;
+    let { isExtensionPage } = contextOptions;
 
-  this.onClose = new Set();
+    this.isExtensionPage = isExtensionPage;
+    this.extension = ExtensionManager.get(extensionId);
+    this.extensionId = extensionId;
+    this.contentWindow = contentWindow;
 
-  let utils = contentWindow.QueryInterface(Ci.nsIInterfaceRequestor)
-                           .getInterface(Ci.nsIDOMWindowUtils);
-  let outerWindowId = utils.outerWindowID;
-  let frameId = contentWindow == contentWindow.top ? 0 : outerWindowId;
-  this.frameId = frameId;
+    let utils = contentWindow.QueryInterface(Ci.nsIInterfaceRequestor)
+                             .getInterface(Ci.nsIDOMWindowUtils);
+    let outerWindowId = utils.outerWindowID;
+    let frameId = contentWindow == contentWindow.top ? 0 : outerWindowId;
+    this.frameId = frameId;
 
-  let mm = getWindowMessageManager(contentWindow);
-  this.messageManager = mm;
+    let mm = getWindowMessageManager(contentWindow);
+    this.messageManager = mm;
+
+    let prin;
+    let contentPrincipal = contentWindow.document.nodePrincipal;
+    let ssm = Services.scriptSecurityManager;
 
-  let prin;
-  let contentPrincipal = contentWindow.document.nodePrincipal;
-  let ssm = Services.scriptSecurityManager;
-  if (ssm.isSystemPrincipal(contentPrincipal)) {
-    // Make sure we don't hand out the system principal by accident.
-    prin = Cc["@mozilla.org/nullprincipal;1"].createInstance(Ci.nsIPrincipal);
-  } else {
     let extensionPrincipal = ssm.createCodebasePrincipal(this.extension.baseURI, {addonId: extensionId});
-    prin = [contentPrincipal, extensionPrincipal];
-  }
+    Object.defineProperty(this, "principal",
+                          {value: extensionPrincipal, enumerable: true, configurable: true});
 
-  if (isExtensionPage) {
-    if (ExtensionManagement.getAddonIdForWindow(this.contentWindow) != extensionId) {
-      throw new Error("Invalid target window for this extension context");
+    if (ssm.isSystemPrincipal(contentPrincipal)) {
+      // Make sure we don't hand out the system principal by accident.
+      prin = Cc["@mozilla.org/nullprincipal;1"].createInstance(Ci.nsIPrincipal);
+    } else {
+      prin = [contentPrincipal, extensionPrincipal];
+    }
+
+    if (isExtensionPage) {
+      if (ExtensionManagement.getAddonIdForWindow(this.contentWindow) != extensionId) {
+        throw new Error("Invalid target window for this extension context");
+      }
+      // This is an iframe with content script API enabled and its principal should be the
+      // contentWindow itself. (we create a sandbox with the contentWindow as principal and with X-rays disabled
+      // because it enables us to create the APIs object in this sandbox object and then copying it
+      // into the iframe's window, see Bug 1214658 for rationale)
+      this.sandbox = Cu.Sandbox(contentWindow, {
+        sandboxPrototype: contentWindow,
+        wantXrays: false,
+        isWebExtensionContentScript: true,
+      });
+    } else {
+      this.sandbox = Cu.Sandbox(prin, {
+        sandboxPrototype: contentWindow,
+        wantXrays: true,
+        isWebExtensionContentScript: true,
+        wantGlobalProperties: ["XMLHttpRequest"],
+      });
+    }
+
+    let delegate = {
+      getSender(context, target, sender) {
+        // Nothing to do here.
+      },
+    };
+
+    let url = contentWindow.location.href;
+    let broker = ExtensionContent.getBroker(mm);
+    // The |sender| parameter is passed directly to the extension.
+    let sender = {id: this.extension.uuid, frameId, url};
+    // Properties in |filter| must match those in the |recipient|
+    // parameter of sendMessage.
+    let filter = {extensionId, frameId};
+    this.messenger = new Messenger(this, broker, sender, filter, delegate);
+
+    this.chromeObj = Cu.createObjectIn(this.sandbox, {defineAs: "browser"});
+
+    // Sandboxes don't get Xrays for some weird compatibility
+    // reason. However, we waive here anyway in case that changes.
+    Cu.waiveXrays(this.sandbox).chrome = this.chromeObj;
+
+    injectAPI(api(this), this.chromeObj);
+
+    // This is an iframe with content script API enabled. (See Bug 1214658 for rationale)
+    if (isExtensionPage) {
+      Cu.waiveXrays(this.contentWindow).chrome = this.chromeObj;
+      Cu.waiveXrays(this.contentWindow).browser = this.chromeObj;
     }
-    // This is an iframe with content script API enabled and its principal should be the
-    // contentWindow itself. (we create a sandbox with the contentWindow as principal and with X-rays disabled
-    // because it enables us to create the APIs object in this sandbox object and then copying it
-    // into the iframe's window, see Bug 1214658 for rationale)
-    this.sandbox = Cu.Sandbox(contentWindow, {
-      sandboxPrototype: contentWindow,
-      wantXrays: false,
-      isWebExtensionContentScript: true,
-    });
-  } else {
-    this.sandbox = Cu.Sandbox(prin, {
-      sandboxPrototype: contentWindow,
-      wantXrays: true,
-      isWebExtensionContentScript: true,
-      wantGlobalProperties: ["XMLHttpRequest"],
-    });
   }
 
-  let delegate = {
-    getSender(context, target, sender) {
-      // Nothing to do here.
-    },
-  };
-
-  let url = contentWindow.location.href;
-  let broker = ExtensionContent.getBroker(mm);
-  // The |sender| parameter is passed directly to the extension.
-  let sender = {id: this.extension.uuid, frameId, url};
-  // Properties in |filter| must match those in the |recipient|
-  // parameter of sendMessage.
-  let filter = {extensionId, frameId};
-  this.messenger = new Messenger(this, broker, sender, filter, delegate);
-
-  this.chromeObj = Cu.createObjectIn(this.sandbox, {defineAs: "browser"});
-
-  // Sandboxes don't get Xrays for some weird compatibility
-  // reason. However, we waive here anyway in case that changes.
-  Cu.waiveXrays(this.sandbox).chrome = this.chromeObj;
-
-  injectAPI(api(this), this.chromeObj);
-
-  // This is an iframe with content script API enabled. (See Bug 1214658 for rationale)
-  if (isExtensionPage) {
-    Cu.waiveXrays(this.contentWindow).chrome = this.chromeObj;
-    Cu.waiveXrays(this.contentWindow).browser = this.chromeObj;
-  }
-}
-
-ExtensionContext.prototype = {
   get cloneScope() {
     return this.sandbox;
-  },
+  }
 
   execute(script, shouldRun) {
     script.tryInject(this.extension, this.contentWindow, this.sandbox, shouldRun);
-  },
-
-  callOnClose(obj) {
-    this.onClose.add(obj);
-  },
-
-  forgetOnClose(obj) {
-    this.onClose.delete(obj);
-  },
+  }
 
   close() {
-    for (let obj of this.onClose) {
-      obj.close();
-    }
+    super.unload();
 
     // Overwrite the content script APIs with an empty object if the APIs objects are still
     // defined in the content window (See Bug 1214658 for rationale).
@@ -338,11 +333,10 @@ ExtensionContext.prototype = {
       Cu.createObjectIn(this.contentWindow, { defineAs: "browser" });
       Cu.createObjectIn(this.contentWindow, { defineAs: "chrome" });
     }
-
     Cu.nukeSandbox(this.sandbox);
     this.sandbox = null;
-  },
-};
+  }
+}
 
 function windowId(window) {
   return window.QueryInterface(Ci.nsIInterfaceRequestor)
diff --git a/toolkit/components/extensions/ExtensionUtils.jsm b/toolkit/components/extensions/ExtensionUtils.jsm
index 0a6269987ac..cf2d4d88bdc 100644
--- a/toolkit/components/extensions/ExtensionUtils.jsm
+++ b/toolkit/components/extensions/ExtensionUtils.jsm
@@ -112,6 +112,53 @@ DefaultWeakMap.prototype = {
   },
 };
 
+class BaseContext {
+  constructor() {
+    this.onClose = new Set();
+  }
+
+  get cloneScope() {
+    throw new Error("Not implemented");
+  }
+
+  get principal() {
+    throw new Error("Not implemented");
+  }
+
+  checkLoadURL(url, options = {}) {
+    let ssm = Services.scriptSecurityManager;
+
+    let flags = ssm.STANDARD;
+    if (!options.allowScript) {
+      flags |= ssm.DISALLOW_SCRIPT;
+    }
+    if (!options.allowInheritsPrincipal) {
+      flags |= ssm.DISALLOW_INHERIT_PRINCIPAL;
+    }
+
+    try {
+      ssm.checkLoadURIStrWithPrincipal(this.principal, url, flags);
+    } catch (e) {
+      return false;
+    }
+    return true;
+  }
+
+  callOnClose(obj) {
+    this.onClose.add(obj);
+  }
+
+  forgetOnClose(obj) {
+    this.onClose.delete(obj);
+  }
+
+  unload() {
+    for (let obj of this.onClose) {
+      obj.close();
+    }
+  }
+}
+
 function LocaleData(data) {
   this.defaultLocale = data.defaultLocale;
   this.selectedLocale = data.selectedLocale;
@@ -786,6 +833,7 @@ this.ExtensionUtils = {
   runSafeSyncWithoutClone,
   runSafe,
   runSafeSync,
+  BaseContext,
   DefaultWeakMap,
   EventManager,
   LocaleData,