The Tor Browser / file revision

 const Cc = Components.classes;

 const Ci = Components.interfaces;

 // 5 seconds.

 const kExpectedDelay1 = 5;

 // 1 second.

 const kExpectedDelay2 = 1;

 var gStartTime1;

 var gStartTime2;

 var timer;

 var observer1 = {

   observe: function observeTC1(subject, topic, data) {

     if (topic == "timer-callback") {

       // Stop timer, so it doesn't repeat (if test runs slowly).

       timer.cancel();

       // Actual delay may not be exact, so convert to seconds and round.

       do_check_eq(Math.round((Date.now() - gStartTime1) / 1000),

                   kExpectedDelay1);

       timer = null;

       do_print("1st timer triggered (before being cancelled). Should not have happened!");

       do_check_true(false);

     }

   }

 };

 var observer2 = {

   observe: function observeTC2(subject, topic, data) {

     if (topic == "timer-callback") {

       // Stop timer, so it doesn't repeat (if test runs slowly).

       timer.cancel();

       // Actual delay may not be exact, so convert to seconds and round.

       do_check_eq(Math.round((Date.now() - gStartTime2) / 1000),

                   kExpectedDelay2);

       timer = null;

       do_test_finished();

     }

   }

 };

 function run_test() {

   do_test_pending();

   timer = Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer);

   // Initialize the timer (with some delay), then cancel it.

   gStartTime1 = Date.now();

   timer.init(observer1, kExpectedDelay1 * 1000, timer.TYPE_REPEATING_PRECISE);

   timer.cancel();

   // Re-initialize the timer (with a different delay).

   gStartTime2 = Date.now();

   timer.init(observer2, kExpectedDelay2 * 1000, timer.TYPE_REPEATING_PRECISE);

 }