new file mode 100644
--- /dev/null
+++ b/browser/base/content/test/sanitize/SiteDataTestUtils.jsm
@@ -0,0 +1,78 @@
+"use strict";
+
+var EXPORTED_SYMBOLS = [
+  "SiteDataTestUtils",
+];
+
+ChromeUtils.import("resource://gre/modules/Services.jsm");
+const {Sanitizer} = ChromeUtils.import("resource:///modules/Sanitizer.jsm", {});
+
+/**
+ * This module assists with tasks around testing functionality that shows
+ * or clears site data.
+ *
+ * Please note that you will have to clean up changes made manually, for
+ * example using SiteDataTestUtils.clear().
+ */
+var SiteDataTestUtils = {
+
+  /**
+   * Adds a new entry to a dummy indexedDB database for the specified origin.
+   *
+   * @param {String} origin - the origin of the site to add test data for
+   *
+   * @returns a Promise that resolves when the data was added successfully.
+   */
+  addToIndexedDB(origin) {
+    return new Promise(resolve => {
+      let uri = Services.io.newURI(origin);
+      let principal = Services.scriptSecurityManager.createCodebasePrincipal(uri, {});
+      let request = indexedDB.openForPrincipal(principal, "TestDatabase", 1);
+      request.onupgradeneeded = function(e) {
+        let db = e.target.result;
+        db.createObjectStore("TestStore", { keyPath: "id" });
+      };
+      request.onsuccess = function(e) {
+        let db = e.target.result;
+        let tx = db.transaction("TestStore", "readwrite");
+        let store = tx.objectStore("TestStore");
+        tx.oncomplete = resolve;
+        store.put({ id: performance.now().toString(), description: "IndexedDB Test"});
+      };
+    });
+  },
+
+  /**
+   * Adds a new cookie for the specified origin, with the specified contents.
+   * The cookie will be valid for one day.
+   *
+   * @param {String} name - the cookie name
+   * @param {String} value - the cookie value
+   */
+  addToCookies(origin, name, value) {
+    let uri = Services.io.newURI(origin);
+    Services.cookies.add(uri.host, uri.pathQueryRef, name, value,
+      false, false, false, Date.now() + 24000 * 60 * 60);
+  },
+
+  /**
+   * Gets the current quota usage for the specified origin.
+   *
+   * @returns a Promise that resolves to an integer with the total
+   *          amount of disk usage by a given origin.
+   */
+  getQuotaUsage(origin) {
+    return new Promise(resolve => {
+      let uri = Services.io.newURI(origin);
+      let principal = Services.scriptSecurityManager.createCodebasePrincipal(uri, {});
+      Services.qms.getUsageForPrincipal(principal, request => resolve(request.result.usage));
+    });
+  },
+
+  /**
+   * Cleans up all site data.
+   */
+  clear() {
+    return Sanitizer.sanitize(["cookies", "cache", "siteSettings", "offlineApps"]);
+  },
+};

--- a/browser/base/moz.build
+++ b/browser/base/moz.build
@@ -16,16 +16,20 @@ with Files('content/docs/sslerrorreport/
 MOCHITEST_MANIFESTS += [
     'content/test/general/mochitest.ini',
 ]
 
 MOCHITEST_CHROME_MANIFESTS += [
     'content/test/chrome/chrome.ini',
 ]
 
+TESTING_JS_MODULES += [
+    'content/test/sanitize/SiteDataTestUtils.jsm',
+]
+
 BROWSER_CHROME_MANIFESTS += [
     'content/test/about/browser.ini',
     'content/test/alerts/browser.ini',
     'content/test/captivePortal/browser.ini',
     'content/test/contextMenu/browser.ini',
     'content/test/favicons/browser.ini',
     'content/test/forms/browser.ini',
     'content/test/general/browser.ini',

--- a/browser/components/preferences/in-content/tests/siteData/browser_clearSiteData.js
+++ b/browser/components/preferences/in-content/tests/siteData/browser_clearSiteData.js
@@ -25,17 +25,17 @@ async function testClearData(clearSiteDa
   // Register some service workers.
   await loadServiceWorkerTestPage(TEST_SERVICE_WORKER_URL);
   await promiseServiceWorkerRegisteredFor(TEST_SERVICE_WORKER_URL);
 
   await openPreferencesViaOpenPreferencesAPI("privacy", { leaveOpen: true });
 
   // Test the initial states.
   let cacheUsage = await SiteDataManager.getCacheSize();
-  let quotaUsage = await getQuotaUsage(TEST_QUOTA_USAGE_ORIGIN);
+  let quotaUsage = await SiteDataTestUtils.getQuotaUsage(TEST_QUOTA_USAGE_ORIGIN);
   let totalUsage = await SiteDataManager.getTotalUsage();
   Assert.greater(cacheUsage, 0, "The cache usage should not be 0");
   Assert.greater(quotaUsage, 0, "The quota usage should not be 0");
   Assert.greater(totalUsage, 0, "The total usage should not be 0");
 
   let initialSizeLabelValue = await ContentTask.spawn(gBrowser.selectedBrowser, null, async function() {
     let sizeLabel = content.document.getElementById("totalSiteDataSize");
     return sizeLabel.textContent;
@@ -122,17 +122,17 @@ async function testClearData(clearSiteDa
     await cookiesClearedPromise;
     await promiseServiceWorkersCleared();
 
     TestUtils.waitForCondition(async function() {
       let usage = await SiteDataManager.getTotalUsage();
       return usage == 0;
     }, "The total usage should be removed");
   } else {
-    quotaUsage = await getQuotaUsage(TEST_QUOTA_USAGE_ORIGIN);
+    quotaUsage = await SiteDataTestUtils.getQuotaUsage(TEST_QUOTA_USAGE_ORIGIN);
     totalUsage = await SiteDataManager.getTotalUsage();
     Assert.greater(quotaUsage, 0, "The quota usage should not be 0");
     Assert.greater(totalUsage, 0, "The total usage should not be 0");
   }
 
   if (clearCache || clearSiteData) {
     // Check that the size label in about:preferences updates after we cleared data.
     await ContentTask.spawn(gBrowser.selectedBrowser, {initialSizeLabelValue}, async function(opts) {

--- a/browser/components/preferences/in-content/tests/siteData/head.js
+++ b/browser/components/preferences/in-content/tests/siteData/head.js
@@ -12,16 +12,19 @@ const TEST_OFFLINE_URL = getRootDirector
 const TEST_SERVICE_WORKER_URL = getRootDirectory(gTestPath).replace("chrome://mochitests/content", TEST_OFFLINE_ORIGIN) + "/service_worker_test.html";
 
 const REMOVE_DIALOG_URL = "chrome://browser/content/preferences/siteDataRemoveSelected.xul";
 
 const { DownloadUtils } = ChromeUtils.import("resource://gre/modules/DownloadUtils.jsm", {});
 const { SiteDataManager } = ChromeUtils.import("resource:///modules/SiteDataManager.jsm", {});
 const { OfflineAppCacheHelper } = ChromeUtils.import("resource:///modules/offlineAppCache.jsm", {});
 
+ChromeUtils.defineModuleGetter(this, "SiteDataTestUtils",
+                               "resource://testing-common/SiteDataTestUtils.jsm");
+
 XPCOMUtils.defineLazyServiceGetter(this, "serviceWorkerManager", "@mozilla.org/serviceworkers/manager;1", "nsIServiceWorkerManager");
 
 function promiseSiteDataManagerSitesUpdated() {
   return TestUtils.topicObserved("sitedatamanager:sites-updated", () => true);
 }
 
 function is_hidden(aElement) {
   var style = aElement.ownerGlobal.getComputedStyle(aElement);
@@ -182,24 +185,16 @@ const mockSiteDataManager = {
   async unregister() {
     await this._SiteDataManager.removeAll();
     this.fakeSites = null;
     this._SiteDataManager._qms = this._originalQMS;
     this._SiteDataManager._removeQuotaUsage = this._originalRemoveQuotaUsage;
   }
 };
 
-function getQuotaUsage(origin) {
-  return new Promise(resolve => {
-    let uri = NetUtil.newURI(origin);
-    let principal = Services.scriptSecurityManager.createCodebasePrincipal(uri, {});
-    Services.qms.getUsageForPrincipal(principal, request => resolve(request.result.usage));
-  });
-}
-
 function promiseCookiesCleared() {
   return TestUtils.topicObserved("cookie-changed", (subj, data) => {
     return data === "cleared";
   });
 }
 
 async function loadServiceWorkerTestPage(url) {
   let tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, url);