typescript

Drag outside of browser window in Firefox

1

- [x] My issue title starts with `Drag outside of browser window in Firefox` - [x] I have read the [README](https://github.com/valor-software/ng2-dragula), especially the ['classic blunders' section](https://github.com/valor-software/ng2-dragula#classic-blunders), and the [dragula docs](https://github.com/bevacqua/dragula)....