File drop in Firefox doesn't always work

[dcervelli]

Originally filed by @Devilly as react-dnd/react-dnd#539.

While working on a project it was noted that the native file drop didn't always work in Firefox. I didn't see any error or whatsoever but I did see the file drop was not handled by the function I had made therefore. While trying to create a testcase I made https://jsfiddle.net/r2mudx7a/ and there quite often the following error is thrown:

Error: Cannot call hover while not dragging.

When trying the fiddle please drag on a text file on the dashed square. In my latest test run I got the error nine times before it finally worked (the file was read and outputted to the console).

[dcervelli]

This works consistently for me if you comment out the Firefox specific code in HTML5Backend.js in beginDragNativeItem/endDragNativeItem. This code was introduced in 2b7b2e3 and made Firefox specific in ea3bcaf.

I added logging and sometimes the mousemove->endDrag is triggered before handleTopDrop and sometimes the opposite.

I've only seen this happen on Windows FF. Repro'd on FF48.0.2.

[emmenko]

I've been getting the same error in our Sentry app, coming from Windows FF (Windows 7, FF 49.0) browsers only.

@dcervelli did you find a solution for this problem, or should we simply "accept" this as it is?

PS: using [email protected] and [email protected]