--- a/devtools/server/tests/browser/browser.ini
+++ b/devtools/server/tests/browser/browser.ini
@@ -90,17 +90,16 @@ skip-if = true # Needs to be updated for
 [browser_perf-recording-actor-01.js]
 skip-if = e10s # Bug 1183605 - devtools/server/tests/browser/ tests are still disabled in E10S
 [browser_perf-recording-actor-02.js]
 skip-if = e10s # Bug 1183605 - devtools/server/tests/browser/ tests are still disabled in E10S
 [browser_perf-samples-01.js]
 [browser_perf-samples-02.js]
 [browser_storage_cookies-duplicate-names.js]
 [browser_storage_dynamic_windows.js]
-uses-unsafe-cpows = true
 [browser_storage_listings.js]
 [browser_storage_updates.js]
 uses-unsafe-cpows = true
 [browser_stylesheets_getTextEmpty.js]
 [browser_stylesheets_nested-iframes.js]
 [browser_timeline.js]
 [browser_timeline_actors.js]
 [browser_timeline_iframes.js]

--- a/devtools/server/tests/browser/browser_storage_dynamic_windows.js
+++ b/devtools/server/tests/browser/browser_storage_dynamic_windows.js
@@ -1,263 +1,190 @@
 /* vim: set ft=javascript ts=2 et sw=2 tw=80: */
 /* Any copyright is dedicated to the Public Domain.
    http://creativecommons.org/publicdomain/zero/1.0/ */
 
 "use strict";
 
-const {StorageFront} = require("devtools/shared/fronts/storage");
-Services.scriptloader.loadSubScript("chrome://mochitests/content/browser/devtools/server/tests/browser/storage-helpers.js", this);
+const { StorageFront } = require("devtools/shared/fronts/storage");
+Services.scriptloader.loadSubScript(
+  "chrome://mochitests/content/browser/devtools/server/tests/browser/storage-helpers.js",
+  this);
 
+// beforeReload references an object representing the initialized state of the
+// storage actor.
 const beforeReload = {
   cookies: {
     "http://test1.example.org": ["c1", "cs2", "c3", "uc1"],
     "http://sectest1.example.org": ["uc1", "cs2"]
   },
-  localStorage: {
-    "http://test1.example.org": ["ls1", "ls2"],
-    "http://sectest1.example.org": ["iframe-u-ls1"]
-  },
-  sessionStorage: {
-    "http://test1.example.org": ["ss1"],
-    "http://sectest1.example.org": ["iframe-u-ss1", "iframe-u-ss2"]
-  },
   indexedDB: {
     "http://test1.example.org": [
       JSON.stringify(["idb1", "obj1"]),
       JSON.stringify(["idb1", "obj2"]),
       JSON.stringify(["idb2", "obj3"]),
     ],
     "http://sectest1.example.org": []
+  },
+  localStorage: {
+    "http://test1.example.org": ["ls1", "ls2"],
+    "http://sectest1.example.org": ["iframe-u-ls1"]
+  },
+  sessionStorage: {
+    "http://test1.example.org": ["ss1"],
+    "http://sectest1.example.org": ["iframe-u-ss1", "iframe-u-ss2"]
   }
 };
 
-async function testStores(data, front) {
-  testWindowsBeforeReload(data);
-
-  // FIXME: Bug 1183581 - browser_storage_dynamic_windows.js IsSafeToRunScript
-  //                      errors when testing reload in E10S mode
-  // yield testReload(front);
-  await testAddIframe(front);
-  await testRemoveIframe(front);
-}
-
-function testWindowsBeforeReload(data) {
-  for (let storageType in beforeReload) {
-    ok(data[storageType], storageType + " storage actor is present");
-    is(Object.keys(data[storageType].hosts).length,
-       Object.keys(beforeReload[storageType]).length,
-       "Number of hosts for " + storageType + "match");
-    for (let host in beforeReload[storageType]) {
-      ok(data[storageType].hosts[host], "Host " + host + " is present");
-    }
-  }
-}
-
-function markOutMatched(toBeEmptied, data, deleted) {
-  if (!Object.keys(toBeEmptied).length) {
-    info("Object empty");
-    return;
+// afterIframeAdded references the items added when an iframe containing storage
+// items is added to the page.
+const afterIframeAdded = {
+  cookies: {
+    "https://sectest1.example.org": [
+      getCookieId("cs2", ".example.org", "/"),
+      getCookieId("sc1", "sectest1.example.org",
+                  "/browser/devtools/server/tests/browser/")
+    ],
+    "http://sectest1.example.org": [
+      getCookieId("sc1", "sectest1.example.org",
+                  "/browser/devtools/server/tests/browser/")
+    ]
+  },
+  indexedDB: {
+    // empty because indexed db creation happens after the page load, so at
+    // the time of window-ready, there was no indexed db present.
+    "https://sectest1.example.org": []
+  },
+  localStorage: {
+    "https://sectest1.example.org": ["iframe-s-ls1"]
+  },
+  sessionStorage: {
+    "https://sectest1.example.org": ["iframe-s-ss1"]
   }
-  ok(Object.keys(data).length,
-     "At least one storage type should be present");
-  for (let storageType in toBeEmptied) {
-    if (!data[storageType]) {
-      continue;
-    }
-    info("Testing for " + storageType);
-    for (let host in data[storageType]) {
-      ok(toBeEmptied[storageType][host], "Host " + host + " found");
-
-      if (!deleted) {
-        for (let item of data[storageType][host]) {
-          let index = toBeEmptied[storageType][host].indexOf(item);
-          ok(index > -1, "Item found - " + item);
-          if (index > -1) {
-            toBeEmptied[storageType][host].splice(index, 1);
-          }
-        }
-        if (!toBeEmptied[storageType][host].length) {
-          delete toBeEmptied[storageType][host];
-        }
-      } else {
-        delete toBeEmptied[storageType][host];
-      }
-    }
-    if (!Object.keys(toBeEmptied[storageType]).length) {
-      delete toBeEmptied[storageType];
-    }
-  }
-}
-
-function testAddIframe(front) {
-  info("Testing if new iframe addition works properly");
-  return new Promise(resolve => {
-    let shouldBeEmpty = {
-      localStorage: {
-        "https://sectest1.example.org": ["iframe-s-ls1"]
-      },
-      sessionStorage: {
-        "https://sectest1.example.org": ["iframe-s-ss1"]
-      },
-      cookies: {
-        "https://sectest1.example.org": [
-          getCookieId("cs2", ".example.org", "/"),
-          getCookieId("sc1", "sectest1.example.org",
-                      "/browser/devtools/server/tests/browser/")
-        ],
-        "http://sectest1.example.org": [
-          getCookieId("sc1", "sectest1.example.org",
-                      "/browser/devtools/server/tests/browser/")
-        ]
-      },
-      indexedDB: {
-        // empty because indexed db creation happens after the page load, so at
-        // the time of window-ready, there was no indexed db present.
-        "https://sectest1.example.org": []
-      },
-      Cache: {
-        "https://sectest1.example.org": []
-      }
-    };
-
-    let onStoresUpdate = data => {
-      info("checking if the hosts list is correct for this iframe addition");
-
-      markOutMatched(shouldBeEmpty, data.added);
+};
 
-      ok(!data.changed || !data.changed.cookies ||
-         !data.changed.cookies["https://sectest1.example.org"],
-         "Nothing got changed for cookies");
-      ok(!data.changed || !data.changed.localStorage ||
-         !data.changed.localStorage["https://sectest1.example.org"],
-         "Nothing got changed for local storage");
-      ok(!data.changed || !data.changed.sessionStorage ||
-         !data.changed.sessionStorage["https://sectest1.example.org"],
-         "Nothing got changed for session storage");
-      ok(!data.changed || !data.changed.indexedDB ||
-         !data.changed.indexedDB["https://sectest1.example.org"],
-         "Nothing got changed for indexed db");
-
-      ok(!data.deleted || !data.deleted.cookies ||
-         !data.deleted.cookies["https://sectest1.example.org"],
-         "Nothing got deleted for cookies");
-      ok(!data.deleted || !data.deleted.localStorage ||
-         !data.deleted.localStorage["https://sectest1.example.org"],
-         "Nothing got deleted for local storage");
-      ok(!data.deleted || !data.deleted.sessionStorage ||
-         !data.deleted.sessionStorage["https://sectest1.example.org"],
-         "Nothing got deleted for session storage");
-      ok(!data.deleted || !data.deleted.indexedDB ||
-         !data.deleted.indexedDB["https://sectest1.example.org"],
-         "Nothing got deleted for indexed db");
-
-      if (!Object.keys(shouldBeEmpty).length) {
-        info("Everything to be received is received.");
-        endTestReloaded();
-      }
-    };
-
-    let endTestReloaded = () => {
-      front.off("stores-update", onStoresUpdate);
-      resolve();
-    };
-
-    front.on("stores-update", onStoresUpdate);
-
-    // eslint-disable-next-line mozilla/no-cpows-in-tests
-    let iframe = gBrowser.contentDocumentAsCPOW.createElement("iframe");
-    iframe.src = ALT_DOMAIN_SECURED + "storage-secured-iframe.html";
-    // eslint-disable-next-line mozilla/no-cpows-in-tests
-    gBrowser.contentDocumentAsCPOW.querySelector("body").appendChild(iframe);
-  });
-}
-
-function testRemoveIframe(front) {
-  info("Testing if iframe removal works properly");
-  return new Promise(resolve => {
-    let shouldBeEmpty = {
-      localStorage: {
-        "http://sectest1.example.org": []
-      },
-      sessionStorage: {
-        "http://sectest1.example.org": []
-      },
-      Cache: {
-        "http://sectest1.example.org": []
-      },
-      indexedDB: {
-        "http://sectest1.example.org": []
-      }
-    };
-
-    let onStoresUpdate = data => {
-      info("checking if the hosts list is correct for this iframe deletion");
-
-      markOutMatched(shouldBeEmpty, data.deleted, true);
-
-      ok(!data.deleted.cookies || !data.deleted.cookies["sectest1.example.org"],
-        "Nothing got deleted for Cookies as " +
-        "the same hostname is still present");
-
-      ok(!data.changed || !data.changed.cookies ||
-         !data.changed.cookies["http://sectest1.example.org"],
-         "Nothing got changed for cookies");
-      ok(!data.changed || !data.changed.localStorage ||
-         !data.changed.localStorage["http://sectest1.example.org"],
-         "Nothing got changed for local storage");
-      ok(!data.changed || !data.changed.sessionStorage ||
-         !data.changed.sessionStorage["http://sectest1.example.org"],
-         "Nothing got changed for session storage");
-
-      ok(!data.added || !data.added.cookies ||
-         !data.added.cookies["http://sectest1.example.org"],
-         "Nothing got added for cookies");
-      ok(!data.added || !data.added.localStorage ||
-         !data.added.localStorage["http://sectest1.example.org"],
-         "Nothing got added for local storage");
-      ok(!data.added || !data.added.sessionStorage ||
-         !data.added.sessionStorage["http://sectest1.example.org"],
-         "Nothing got added for session storage");
-
-      if (!Object.keys(shouldBeEmpty).length) {
-        info("Everything to be received is received.");
-        endTestReloaded();
-      }
-    };
-
-    let endTestReloaded = () => {
-      front.off("stores-update", onStoresUpdate);
-      resolve();
-    };
-
-    front.on("stores-update", onStoresUpdate);
-
-    ContentTask.spawn(gBrowser.selectedBrowser, {}, () => {
-      for (let iframe of content.document.querySelectorAll("iframe")) {
-        if (iframe.src.startsWith("http:")) {
-          iframe.remove();
-          break;
-        }
-      }
-    });
-  });
-}
+// afterIframeRemoved references the items deleted when an iframe containing
+// storage items is removed from the page.
+const afterIframeRemoved = {
+  cookies: {
+    "http://sectest1.example.org": []
+  },
+  indexedDB: {
+    "http://sectest1.example.org": []
+  },
+  localStorage: {
+    "http://sectest1.example.org": []
+  },
+  sessionStorage: {
+    "http://sectest1.example.org": []
+  },
+};
 
 add_task(async function() {
   await openTabAndSetupStorage(MAIN_DOMAIN + "storage-dynamic-windows.html");
 
   initDebuggerServer();
   let client = new DebuggerClient(DebuggerServer.connectPipe());
   let form = await connectDebuggerClient(client);
   let front = StorageFront(client, form);
   let data = await front.listStores();
+
   await testStores(data, front);
 
   await clearStorage();
 
   // Forcing GC/CC to get rid of docshells and windows created by this test.
   forceCollections();
   await client.close();
   forceCollections();
   DebuggerServer.destroy();
   forceCollections();
 });
+
+async function testStores(data, front) {
+  testWindowsBeforeReload(data);
+
+  await testAddIframe(front);
+  await testRemoveIframe(front);
+}
+
+function testWindowsBeforeReload(data) {
+  for (let storageType in beforeReload) {
+    ok(data[storageType], `${storageType} storage actor is present`);
+    is(Object.keys(data[storageType].hosts).length,
+       Object.keys(beforeReload[storageType]).length,
+        `Number of hosts for ${storageType} match`);
+    for (let host in beforeReload[storageType]) {
+      ok(data[storageType].hosts[host], `Host ${host} is present`);
+    }
+  }
+}
+
+async function testAddIframe(front) {
+  info("Testing if new iframe addition works properly");
+
+  let update = front.once("stores-update");
+
+  await ContentTask.spawn(gBrowser.selectedBrowser, ALT_DOMAIN_SECURED,
+    secured => {
+      let doc = content.document;
+
+      let iframe = doc.createElement("iframe");
+      iframe.src = secured + "storage-secured-iframe.html";
+
+      doc.querySelector("body").appendChild(iframe);
+    }
+  );
+
+  let data = await update;
+
+  validateStorage(data, afterIframeAdded, "added");
+}
+
+async function testRemoveIframe(front) {
+  info("Testing if iframe removal works properly");
+
+  let update = front.once("stores-update");
+
+  await ContentTask.spawn(gBrowser.selectedBrowser, {}, () => {
+    for (let iframe of content.document.querySelectorAll("iframe")) {
+      if (iframe.src.startsWith("http:")) {
+        iframe.remove();
+        break;
+      }
+    }
+  });
+
+  let data = await update;
+
+  validateStorage(data, afterIframeRemoved, "deleted");
+}
+
+function validateStorage(actual, expected, category = "") {
+  if (category) {
+    for (let cat of ["added", "changed", "deleted"]) {
+      if (cat === category) {
+        ok(actual[cat], `Data from the iframe has been ${cat}.`);
+      } else {
+        ok(!actual[cat], `No data was ${cat}.`);
+      }
+    }
+  }
+
+  for (let [type, expectedData] of Object.entries(expected)) {
+    let actualData = category ? actual[category][type] : actual[type];
+
+    ok(actualData, `${type} contains data.`);
+
+    let actualKeys = Object.keys(actualData);
+    let expectedKeys = Object.keys(expectedData);
+    is(actualKeys.length, expectedKeys.length, `${type} data is the correct length.`);
+
+    for (let [key, dataValues] of Object.entries(expectedData)) {
+      ok(actualData[key], `${type} data contains the key ${key}.`);
+
+      for (let dataValue of dataValues) {
+        ok(actualData[key].includes(dataValue),
+          `${type}[${key}] contains "${dataValue}".`);
+      }
+    }
+  }
+}