--- a/testing/marionette/client/marionette_driver/marionette.py
+++ b/testing/marionette/client/marionette_driver/marionette.py
@@ -1229,45 +1229,66 @@ class Marionette(object):
         If a script does not return in the specified amount of time,
         a ScriptTimeoutException is raised.
 
         :param timeout: The maximum number of milliseconds an asynchronous
             script can run without causing an ScriptTimeoutException to
             be raised
 
         """
-        self._send_message("timeouts", {"script": timeout})
+        try:
+            self._send_message("timeouts", {"script": timeout})
+        except errors.MarionetteException as e:
+            # remove when 52.0a is stable
+            if "Not a Number" in e.message:
+                self._send_message("timeouts", {"type": "script", "ms": timeout})
+            else:
+                raise e
 
     def set_search_timeout(self, timeout):
         """Sets a timeout for the find methods.
 
         When searching for an element using
         either :class:`Marionette.find_element` or
         :class:`Marionette.find_elements`, the method will continue
         trying to locate the element for up to timeout ms. This can be
         useful if, for example, the element you're looking for might
         not exist immediately, because it belongs to a page which is
         currently being loaded.
 
         :param timeout: Timeout in milliseconds.
 
         """
-        self._send_message("timeouts", {"implicit": timeout})
+        try:
+            self._send_message("timeouts", {"implicit": timeout})
+        except errors.MarionetteException as e:
+            # remove when 52.0a is stable
+            if "Not a Number" in e.message:
+                self._send_message("timeouts", {"type": "implicit", "ms": timeout})
+            else:
+                raise e
 
     def set_page_load_timeout(self, timeout):
         """Sets a timeout for loading pages.
 
         A page load timeout specifies the amount of time the Marionette
         instance should wait for a page load operation to complete. A
         ``TimeoutException`` is returned if this limit is exceeded.
 
         :param timeout: Timeout in milliseconds.
 
         """
-        self._send_message("timeouts", {"page load": timeout})
+        try:
+            self._send_message("timeouts", {"page load": timeout})
+        except errors.MarionetteException as e:
+            # remove when 52.0a is stable
+            if "Not a Number" in e.message:
+                self._send_message("timeouts", {"type": "page load", "ms": timeout})
+            else:
+                raise e
 
     @property
     def current_window_handle(self):
         """Get the current window's handle.
 
         Returns an opaque server-assigned identifier to this window
         that uniquely identifies it within this Marionette instance.
         This can be used to switch to this window at a later point.