From the demo today at the devtools work week, @mykmelez added an app to the simulator. After he did this, the file input continued to list the selected path to the manifest file.
In my opinion, there probably isn't a need to re-add an already added app via URL, so the input should be cleared after the app is successfully added.
document.getElementById("form-add-app").reset() would do this, right?
Closed by pull request #376.