When sending a unicode string to the marionette server using the client like this: marionette.send_keys(u"\ue007") it gets processed incorrectly once received. This should be understood as the ENTER key, but instead turns into a checkmark in B2G Desktop, or a square in B@G on the phone. Most likely cause is packing/unpacking in JSON protocol layer.
I no longer get the checkmark, now I see a the U+e007 PUA icon. Even if I send the unicode directly to the sendKeys icon, it displays the E007 icon, instead of translating that to an ENTER key
This should be fixed from bug 751637