--- a/browser/base/content/test/general/browser_aboutCertError.js
+++ b/browser/base/content/test/general/browser_aboutCertError.js
@@ -140,18 +140,17 @@ add_task(function* checkWrongSystemTimeW
   let formatter = new Intl.DateTimeFormat();
 
   // pretend we have a positively skewed (ahead) system time
   let serverDate = new Date("2015/10/27");
   let serverDateFmt = formatter.format(serverDate);
   let localDateFmt = formatter.format(new Date());
 
   let skew = Math.floor((Date.now() - serverDate.getTime()) / 1000);
-  yield new Promise(r => SpecialPowers.pushPrefEnv({set:
-    [[PREF_BLOCKLIST_CLOCK_SKEW_SECONDS, skew]]}, r));
+  yield SpecialPowers.pushPrefEnv({set: [[PREF_BLOCKLIST_CLOCK_SKEW_SECONDS, skew]]});
 
   info("Loading a bad cert page with a skewed clock");
   let message = yield Task.spawn(setUpPage);
 
   isnot(message.divDisplay, "none", "Wrong time message information is visible");
   ok(message.text.includes("because your clock appears to show the wrong time"),
      "Correct error message found");
   ok(message.text.includes("expired.example.com"), "URL found in error message");
@@ -162,47 +161,44 @@ add_task(function* checkWrongSystemTimeW
   yield BrowserTestUtils.removeTab(gBrowser.selectedTab);
 
   // pretend we have a negatively skewed (behind) system time
   serverDate = new Date();
   serverDate.setYear(serverDate.getFullYear() + 1);
   serverDateFmt = formatter.format(serverDate);
 
   skew = Math.floor((Date.now() - serverDate.getTime()) / 1000);
-  yield new Promise(r => SpecialPowers.pushPrefEnv({set:
-    [[PREF_BLOCKLIST_CLOCK_SKEW_SECONDS, skew]]}, r));
+  yield SpecialPowers.pushPrefEnv({set: [[PREF_BLOCKLIST_CLOCK_SKEW_SECONDS, skew]]});
 
   info("Loading a bad cert page with a skewed clock");
   message = yield Task.spawn(setUpPage);
 
   isnot(message.divDisplay, "none", "Wrong time message information is visible");
   ok(message.text.includes("because your clock appears to show the wrong time"),
      "Correct error message found");
   ok(message.text.includes("expired.example.com"), "URL found in error message");
   ok(message.systemDate.includes(localDateFmt), "correct local date displayed");
   ok(message.actualDate.includes(serverDateFmt), "correct server date displayed");
 
   yield BrowserTestUtils.removeTab(gBrowser.selectedTab);
 
   // pretend we only have a slightly skewed system time, four hours
   skew = 60 * 60 * 4;
-  yield new Promise(r => SpecialPowers.pushPrefEnv({set:
-    [[PREF_BLOCKLIST_CLOCK_SKEW_SECONDS, skew]]}, r));
+  yield SpecialPowers.pushPrefEnv({set: [[PREF_BLOCKLIST_CLOCK_SKEW_SECONDS, skew]]});
 
   info("Loading a bad cert page with an only slightly skewed clock");
   message = yield Task.spawn(setUpPage);
 
   is(message.divDisplay, "none", "Wrong time message information is not visible");
 
   yield BrowserTestUtils.removeTab(gBrowser.selectedTab);
 
   // now pretend we have no skewed system time
   skew = 0;
-  yield new Promise(r => SpecialPowers.pushPrefEnv({set:
-    [[PREF_BLOCKLIST_CLOCK_SKEW_SECONDS, skew]]}, r));
+  yield SpecialPowers.pushPrefEnv({set: [[PREF_BLOCKLIST_CLOCK_SKEW_SECONDS, skew]]});
 
   info("Loading a bad cert page with no skewed clock");
   message = yield Task.spawn(setUpPage);
 
   is(message.divDisplay, "none", "Wrong time message information is not visible");
 
   yield BrowserTestUtils.removeTab(gBrowser.selectedTab);
 });