--- a/toolkit/components/url-classifier/tests/browser/classifierHelper.js
+++ b/toolkit/components/url-classifier/tests/browser/classifierHelper.js
@@ -138,17 +138,17 @@ classifierHelper.removeUrlFromDB = funct
     });
 
   return classifierHelper._update(testUpdate);
 };
 
 // This API is used to expire all add/sub chunks we have updated
 // by using addUrlToDB and removeUrlFromDB.
 // Returns a Promise.
-classifierHelper.resetDB = function() {
+classifierHelper.resetDatabase = function() {
   var testUpdate = "";
   for (var update of classifierHelper._updatesToCleanup) {
     if (testUpdate.includes(update.db))
       continue;
 
     testUpdate +=
       "n:1000\n" +
       "i:" + update.db + "\n" +
@@ -209,12 +209,12 @@ classifierHelper._cleanup = function() {
   for (var pref in PREFS) {
     Services.prefs.clearUserPref(pref);
   }
 
   if (!classifierHelper._updatesToCleanup) {
     return Promise.resolve();
   }
 
-  return classifierHelper.resetDB();
+  return classifierHelper.resetDatabase();
 };
 // Cleanup will be called at end of each testcase to remove all the urls added to database.
 registerCleanupFunction(classifierHelper._cleanup);

--- a/toolkit/components/url-classifier/tests/mochitest/classifierHelper.js
+++ b/toolkit/components/url-classifier/tests/mochitest/classifierHelper.js
@@ -103,32 +103,40 @@ classifierHelper.removeUrlFromDB = funct
       });
 
     classifierHelper._update(testUpdate, resolve, reject);
   });
 };
 
 // This API is used to expire all add/sub chunks we have updated
 // by using addUrlToDB and removeUrlFromDB.
-classifierHelper.resetDB = function() {
-  return new Promise(function(resolve, reject) {
-    var testUpdate = "";
-    for (var update of classifierHelper._updatesToCleanup) {
-      if (testUpdate.includes(update.db))
-        continue;
+classifierHelper.resetDatabase = function() {
+  function removeDatabase() {
+    return new Promise(function(resolve, reject) {
+      var testUpdate = "";
+      for (var update of classifierHelper._updatesToCleanup) {
+        if (testUpdate.includes(update.db))
+          continue;
 
-      testUpdate +=
-        "n:1000\n" +
-        "i:" + update.db + "\n" +
-        "ad:" + ADD_CHUNKNUM + "\n" +
-        "sd:" + SUB_CHUNKNUM + "\n"
-    }
+        testUpdate +=
+          "n:1000\n" +
+          "i:" + update.db + "\n" +
+          "ad:" + ADD_CHUNKNUM + "\n" +
+          "sd:" + SUB_CHUNKNUM + "\n"
+      }
 
-    classifierHelper._update(testUpdate, resolve, reject);
-  });
+      classifierHelper._update(testUpdate, resolve, reject);
+    });
+  }
+
+  // Remove and then reload will ensure both database and cache will
+  // be cleared.
+  return Promise.resolve()
+    .then(removeDatabase)
+    .then(classifierHelper.reloadDatabase);
 };
 
 classifierHelper.reloadDatabase = function() {
   return new Promise(function(resolve, reject) {
     gScript.addMessageListener("reloadSuccess", function handler() {
       gScript.removeMessageListener('reloadSuccess', handler);
       resolve();
     });
@@ -190,12 +198,12 @@ classifierHelper._cleanup = function() {
   for (var pref in PREFS) {
     SpecialPowers.clearUserPref(pref);
   }
 
   if (!classifierHelper._updatesToCleanup) {
     return Promise.resolve();
   }
 
-  return classifierHelper.resetDB();
+  return classifierHelper.resetDatabase();
 };
 
 classifierHelper._setup();

--- a/toolkit/components/url-classifier/tests/mochitest/test_bug1254766.html
+++ b/toolkit/components/url-classifier/tests/mochitest/test_bug1254766.html
@@ -75,17 +75,17 @@ function setup() {
     addCompletionToServer(MALWARE_LIST, MALWARE_HOST2, GETHASH_URL),
     addCompletionToServer(UNWANTED_LIST, UNWANTED_HOST1, GETHASH_URL),
     addCompletionToServer(UNWANTED_LIST, UNWANTED_HOST2, GETHASH_URL),
   ]);
 }
 
 // Reset function in helper try to simulate the behavior we restart firefox
 function reset() {
-  return classifierHelper.resetDB()
+  return classifierHelper.resetDatabase()
     .catch(err => {
       ok(false, "Couldn't update classifier. Error code: " + errorCode);
       // Abort test.
       SimpleTest.finish();
     });
 }
 
 function updateUnusedUrl() {

--- a/toolkit/components/url-classifier/tests/mochitest/test_cachemiss.html
+++ b/toolkit/components/url-classifier/tests/mochitest/test_cachemiss.html
@@ -68,17 +68,17 @@ function addPrefixToDB(list, url) {
       ok(false, "Couldn't update classifier. Error code: " + err);
       // Abort test.
       SimpleTest.finish();
     });
 }
 
 // manually reset DB to make sure next test won't be affected by cache.
 function reset() {
-  return classifierHelper.resetDB;
+  return classifierHelper.resetDatabase();
 }
 
 // This test has to come before testPositiveCache to ensure gethash server doesn't
 // contain completions.
 function testNegativeCache() {
   shouldLoad = true;
 
   function setup() {

--- a/toolkit/components/url-classifier/tests/mochitest/test_classifier.html
+++ b/toolkit/components/url-classifier/tests/mochitest/test_classifier.html
@@ -13,17 +13,17 @@
 <pre id="test">
 
 <script class="testbody" type="text/javascript">
 
 var firstLoad = true;
 
 // Add some URLs to the malware database.
 // Note that we intentionally don't touch test-phish-simple, and will
-// use the URL registered by addMozEntries().  Otherwise, classifierHelper.resetDB()
+// use the URL registered by addMozEntries().  Otherwise, classifierHelper.resetDatabase()
 // will reset this table, and waitForInit() can't find the known phishing
 // URL in test-phish-simple, breaking the tests following this one.
 var testData = [
   { url: "malware.example.com/",
     db: "test-malware-simple"
   },
   { url: "unwanted.example.com/",
     db: "test-unwanted-simple"

--- a/toolkit/components/url-classifier/tests/mochitest/test_gethash.html
+++ b/toolkit/components/url-classifier/tests/mochitest/test_gethash.html
@@ -76,17 +76,17 @@ function setup() {
     addPrefixToDB(UNWANTED_LIST, UNWANTED_HOST),
     addCompletionToServer(MALWARE_LIST, MALWARE_HOST, GETHASH_URL),
     addCompletionToServer(UNWANTED_LIST, UNWANTED_HOST, GETHASH_URL),
   ]);
 }
 
 // manually reset DB to make sure next test won't be affected by cache.
 function reset() {
-  return classifierHelper.resetDB;
+  return classifierHelper.resetDatabase();
 }
 
 function runTest() {
   Promise.resolve()
     // This test resources get blocked when gethash returns successfully
     .then(classifierHelper.waitForInit)
     .then(setup)
     .then(() => loadTestFrame("testFrame1"))