When this is implemented in Gecko, perhaps [a test from Chromium](https://source.chromium.org/chromium/chromium/src/+/master:third_party/blink/web_tests/fast/events/drag-downloadURL.html?q=DownloadURL&ss=chromium%2Fchromium%2Fsrc) can be upstreamed to WPT.
Bug 570164 Comment 19 Edit History
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When this is implemented in Gecko, perhaps [a test from Chromium](https://source.chromium.org/chromium/chromium/src/+/master:third_party/blink/web_tests/fast/events/drag-downloadURL.html?q=DownloadURL&ss=chromium%2Fchromium%2Fsrc) can be lifted to a WPT.