The dropzone attribute is not implemented in any browser.

WebKit and Blink have implemented prefixed versions of the attribute, webkitdropzone. I plan to remove the Blink implementation because it hasn't gained much use -- we had a serious bug and it has gone unnoticed for at least a few releases.

In general, I think dropzone is a bit out of place, because it attempts to specify drag-and-drop behavior declaratively, but an application that implements drag-and-drop still needs to use script to handle a drop.

I'm happy to help (e.g., edit the spec and remove WPT files), if this change is agreed upon.