diff --git a/calendar/test/browser/browser.ini b/calendar/test/browser/browser.ini
index 5012ac0c1a..6a4ae5f949 100644
--- a/calendar/test/browser/browser.ini
+++ b/calendar/test/browser/browser.ini
@@ -18,5 +18,6 @@ support-files = data/**
 [browser_localICS.js]
 [browser_tabs.js]
 [browser_timezones.js]
+skip-if = debug
 [browser_todayPane.js]
 [browser_todayPane_visibility.js]
diff --git a/mail/components/preferences/test/browser/browser_general.js b/mail/components/preferences/test/browser/browser_general.js
index 3244ecdbdf..5ecba4c873 100644
--- a/mail/components/preferences/test/browser/browser_general.js
+++ b/mail/components/preferences/test/browser/browser_general.js
@@ -2,6 +2,14 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, you can obtain one at http://mozilla.org/MPL/2.0/. */
 
+add_task(async () => {
+  // Temporarily disable `Once` StaticPrefs check for this test so that we
+  // can change layers.acceleration.disabled without debug builds failing.
+  await SpecialPowers.pushPrefEnv({
+    set: [["preferences.force-disable.check.once.policy", true]],
+  });
+});
+
 add_task(async () => {
   await testCheckboxes(
     "paneGeneral",
diff --git a/mozharness/unittests/thunderbird_extra.py b/mozharness/unittests/thunderbird_extra.py
index 07dcef7287..9e0a791c71 100644
--- a/mozharness/unittests/thunderbird_extra.py
+++ b/mozharness/unittests/thunderbird_extra.py
@@ -27,6 +27,7 @@ config = {
     },
     "all_mochitest_suites": {
         "browser-chrome-thunderbird": ["--flavor=browser",
-                                       "--subsuite=thunderbird"],
+                                       "--subsuite=thunderbird",
+                                       "--leak-threshold=10485760"],
     },
 }
diff --git a/taskcluster/ci/test/test-platforms.yml b/taskcluster/ci/test/test-platforms.yml
index 1671f3905c..935b1121ad 100644
--- a/taskcluster/ci/test/test-platforms.yml
+++ b/taskcluster/ci/test/test-platforms.yml
@@ -40,6 +40,7 @@ linux64/debug:
     test-sets:
         - gtest-tests
         - marionette-tests
+        - mochitest-tests
         - mozmill-tests
         - xpcshell-tests
 
@@ -57,6 +58,7 @@ linux32/debug:
     test-sets:
         - gtest-tests
         - marionette-tests
+        - mochitest-tests
         - mozmill-tests
         - xpcshell-tests
 
@@ -86,6 +88,7 @@ windows7-32/debug:
     test-sets:
         - gtest-tests
         - marionette-tests
+        - mochitest-tests
         - mozmill-tests
         - xpcshell-tests
 
@@ -113,6 +116,7 @@ windows10-64/debug:
     test-sets:
         - gtest-tests
         - marionette-tests
+        - mochitest-tests
         - mozmill-tests
         - xpcshell-tests
 
@@ -123,6 +127,7 @@ macosx1014-64/debug:
     test-sets:
         - gtest-tests
         - marionette-tests
+        - mochitest-tests
         - mozmill-tests
         - xpcshell-tests