User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_2) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36

Steps to reproduce:

1. Create an element containing a shadow root
2. Set the element to draggable=true
3. Add a dragstart listener to the element
4. Drag from any element inside the shadow root

Test/example: http://jsfiddle.net/L0vf39pb/

Actual results:

The dragstart listener is called properly when dragging from any element outside the shadow root but never triggered when dragging an element inside the shadow root.

Expected results:

Shadow roots should not prevent dragging. Dragging any element inside the shadow root should also start the drag operation.

Related Webkit issue, recently fixed: https://bugs.webkit.org/show_bug.cgi?id=136836
Provided test passes in Chrome stable, Safari Tech Preview. Fails in stable Safari as the linked fixed has not been included yet.

I can reproduce this issue on all versions of Firefox: nightly 66.0a1, beta 65.0b12, release 64.0.2 and different OS's: windows 10, Mac OS X, Ubuntu.

Before this change, only elements inside the shadow root tree were scanned for the
draggable=true attribute. We now check the flattened tree instead so an element
inside a shadow root can start a drag for an element containing the shadow root.

Artur, thanks so much for this fix!

https://hg.mozilla.org/mozilla-central/rev/23e432bdaf62

Since the status are different for nightly and release, what's the status for beta?
For more information, please visit auto_nag documentation.

Verified - Fixed on latest Nightly 68.0a1 (2019-05-14) (64-bit) on Windows 10, Mac OS 10.14 and Ubuntu 18.04.