I don't yet have STR, but it's happened to me twice in the last 2 days. After using my browser for some period of time, the browser ends up stuck in a d&d session which is never ended, and attempts to drag things stop working. Opening the browser console and running Cc["@mozilla.org/widget/dragservice;1"].getService(Ci.nsIDragService).getCurrentSession().endDragSession(true) causes the browser to start accepting new drags again.

I don't know exactly what causes this to occur, but I figured I'd file a bug anyway.

I'm running Fedora using X11, and have Fission enabled.

ni? :stransky as AFAICT you've been working on the dragservice/gtk code recently.

Yes. Would be great to have some STR or log from the session. Please try to run Firefox with:

MOZ_LOG="WidgetDrag:5"

env variable and attach the log here when you manage to reproduce it.
Thanks.

Should be dupe of Bug 1735348.