Firefox is terminated during Drag & Drop due to protocol error - mutter selects 'Ask' method
See https://bugzilla.mozilla.org/show_bug.cgi?id=1733317
When pasting an image from Nautilus to Firefox (to http://onpaste.com/ site) and user press 'ALT', a question mark is shown and Mutter selects 'ASK' D&D method. When Drop is performed Firefox is terminated with protocol error.
But Firefox states it doesn't want the 'ASK' method:
[2618374.932] wl_data_offer@4278190081.action(4)
[2618375.011] -> wl_data_offer@4278190081.set_actions(7, 2)
[2618375.020] -> wl_data_offer@4278190081.accept(25200, "text/plain")
This is Mutter bug only, KWin works as expected.