--- a/testing/mochitest/runtests.py
+++ b/testing/mochitest/runtests.py
@@ -46,17 +46,17 @@ from manifestparser.filters import (
     pathprefix,
     subsuite,
     tags,
 )
 
 try:
     from marionette_driver.addons import Addons
     from marionette_harness import Marionette
-except ImportError, e:
+except ImportError as e:
     # Defer ImportError until attempt to use Marionette
     def reraise(*args, **kwargs):
         raise(e)
     Marionette = reraise
 
 from leaks import ShutdownLeaks, LSANLeaks
 from mochitest_options import (
     MochitestArgumentParser, build_obj, get_default_valgrind_suppression_files
@@ -845,17 +845,17 @@ class MochitestDesktop(object):
         return test_environment(**kwargs)
 
     def extraPrefs(self, extraPrefs):
         """interpolate extra preferences from option strings"""
 
         try:
             return dict(parseKeyValue(extraPrefs, context='--setpref='))
         except KeyValueParseError as e:
-            print str(e)
+            print(str(e))
             sys.exit(1)
 
     def getFullPath(self, path):
         " Get an absolute path relative to self.oldcwd."
         return os.path.normpath(
             os.path.join(
                 self.oldcwd,
                 os.path.expanduser(path)))
@@ -2218,17 +2218,17 @@ toolbar#nav-bar {
         if not options.runByDir:
             return self.runMochitests(options, testsToRun)
 
         # code for --run-by-dir
         dirs = self.getDirectories(options)
 
         result = 1  # default value, if no tests are run.
         for d in dirs:
-            print "dir: %s" % d
+            print("dir: %s" % d)
 
             # BEGIN LEAKCHECK HACK
             # Leak checking was broken in mochitest unnoticed for a length of time. During
             # this time, several leaks slipped through. The leak checking was fixed by bug
             # 1325148, but it couldn't land until all the regressions were also fixed or
             # backed out. Rather than waiting and risking new regressions, in the meantime
             # this code will selectively disable leak checking on flavors/directories where
             # known regressions exist. At least this way we can prevent further damage while
@@ -2266,30 +2266,30 @@ toolbar#nav-bar {
 
             if result == -1:
                 break
 
         e10s_mode = "e10s" if options.e10s else "non-e10s"
 
         # printing total number of tests
         if options.flavor == 'browser':
-            print "TEST-INFO | checking window state"
-            print "Browser Chrome Test Summary"
-            print "\tPassed: %s" % self.countpass
-            print "\tFailed: %s" % self.countfail
-            print "\tTodo: %s" % self.counttodo
-            print "\tMode: %s" % e10s_mode
-            print "*** End BrowserChrome Test Results ***"
+            print("TEST-INFO | checking window state")
+            print("Browser Chrome Test Summary")
+            print("\tPassed: %s" % self.countpass)
+            print("\tFailed: %s" % self.countfail)
+            print("\tTodo: %s" % self.counttodo)
+            print("\tMode: %s" % e10s_mode)
+            print("*** End BrowserChrome Test Results ***")
         else:
-            print "0 INFO TEST-START | Shutdown"
-            print "1 INFO Passed:  %s" % self.countpass
-            print "2 INFO Failed:  %s" % self.countfail
-            print "3 INFO Todo:    %s" % self.counttodo
-            print "4 INFO Mode:    %s" % e10s_mode
-            print "5 INFO SimpleTest FINISHED"
+            print("0 INFO TEST-START | Shutdown")
+            print("1 INFO Passed:  %s" % self.countpass)
+            print("2 INFO Failed:  %s" % self.countfail)
+            print("3 INFO Todo:    %s" % self.counttodo)
+            print("4 INFO Mode:    %s" % e10s_mode)
+            print("5 INFO SimpleTest FINISHED")
 
         return result
 
     def doTests(self, options, testsToFilter=None):
         # A call to initializeLooping method is required in case of --run-by-dir or --bisect-chunk
         # since we need to initialize variables for each loop.
         if options.bisectChunk or options.runByDir:
             self.initializeLooping(options)