--- a/testing/puppeteer/firefox/firefox_puppeteer/__init__.py
+++ b/testing/puppeteer/firefox/firefox_puppeteer/__init__.py
@@ -61,17 +61,17 @@ class Puppeteer(object):
         """
 
     @property
     def platform(self):
         """Returns the lowercased platform name.
 
         :returns: Platform name
         """
-        return self.marionette.session_capabilities['platformName'].lower()
+        return self.marionette.session_capabilities['platformName']
 
     @use_class_as_property('api.prefs.Preferences')
     def prefs(self):
         """
         Provides an api for setting and inspecting preferences, as see in
         about:config.
 
         See the :class:`~api.prefs.Preferences` reference.

--- a/testing/puppeteer/firefox/firefox_puppeteer/api/keys.py
+++ b/testing/puppeteer/firefox/firefox_puppeteer/api/keys.py
@@ -8,13 +8,13 @@ import marionette_driver
 class Keys(marionette_driver.keys.Keys):
     """Proxy to marionette's keys with an "accel" provided for convenience
     testing across platforms."""
 
     def __init__(self, marionette_getter):
         self.marionette_getter = marionette_getter
 
         caps = self.marionette_getter().session_capabilities
-        self.isDarwin = caps['platformName'] == 'DARWIN'
+        self.isDarwin = caps['platformName'] == 'darwin'
 
     @property
     def ACCEL(self):
         return self.META if self.isDarwin else self.CONTROL

--- a/testing/puppeteer/firefox/firefox_puppeteer/ui/windows.py
+++ b/testing/puppeteer/firefox/firefox_puppeteer/ui/windows.py
@@ -393,17 +393,17 @@ class BaseWindow(BaseLib):
         :param ctrl: Optional, If `True`, the `Ctrl` modifier key is pressed. Defaults to `False`.
 
         :param meta: Optional, If `True`, the `Meta` modifier key is pressed. Defaults to `False`.
 
         :param shift: Optional, If `True`, the `Shift` modifier key is pressed.
          Defaults to `False`.
         """
 
-        platform = self.marionette.session_capabilities['platformName'].lower()
+        platform = self.marionette.session_capabilities['platformName']
 
         keymap = {
             'accel': Keys.META if platform == 'darwin' else Keys.CONTROL,
             'alt': Keys.ALT,
             'cmd': Keys.COMMAND,
             'ctrl': Keys.CONTROL,
             'meta': Keys.META,
             'shift': Keys.SHIFT,