Cursor invisible after drag-n-drop in Firefox

1. Load http://prosemirror.net/
2. Drag logo into the ProseMirror editor example
3. Click somewhere in the editor
4. Type "foo"

Expected: Cursor should appear after step 3, and "foo" should be inserted

Actual: Cursor never appears, but "foo" is still inserted at the proper location

Appears to be a bug with Firefox's contenteditable implementation (there are several on bugzilla regarding the cursor). I haven't dug into it too much yet, but clicking elsewhere (eg, the "A toolkit..." title) and then clicking back into the editor will show the cursor again.