With the extension enabled, nautilus outputs the following repeatedly:
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/syncthing_gtk/nautilusplugin.py", line 303, in get_background_items
path = self._get_path(item).rstrip("/")
File "/usr/lib/python3/dist-packages/syncthing_gtk/nautilusplugin.py", line 117, in _get_path
return file.get_location().get_path().decode('utf-8')
AttributeError: 'str' object has no attribute 'decode'
Looks like code that hasn't been updated to work on Python 3...