Check for proxy bypasses with new HTML Drag and Drop API
We had issues in the past with drag and drop bypassing our proxy settings. There is a new API that got implemented which can do the things the old one did and more (see: https://bugzilla.mozilla.org/show_bug.cgi?id=906420, https://bugzilla.mozilla.org/show_bug.cgi?id=1289255, and https://bugzilla.mozilla.org/show_bug.cgi?id=1298243). We should assure that our old defense against proxy bypass holds.