Bug 1446116 Disable timer jitter on test_ext_alarms.js r=gbrown

MozReview-Commit-ID: 27Z3vIejv8y

--HG--
extra : rebase_source : c373fd87e7a61a31582f874f8056d08eed32b7e9

toolkit/components/extensions/test/xpcshell/test_ext_alarms.js

@@ -90,6 +90,7 @@ add_task(async function test_alarm_fires_with_when() {
     },
   });
 
+  Services.prefs.setBoolPref("privacy.resistFingerprinting.reduceTimerPrecision.jitter", false);
   await extension.startup();
   await extension.awaitFinish("alarm-when");
 
@@ -97,6 +98,7 @@ add_task(async function test_alarm_fires_with_when() {
   // reply finishes.
   await new Promise(resolve => setTimeout(resolve, 0));
   await extension.unload();
+  Services.prefs.clearUserPref("privacy.resistFingerprinting.reduceTimerPrecision.jitter");
 });
 
 add_task(async function test_alarm_clear_non_matching_name() {