This is quite weird. It was working all fine last week, but today I discovered every time I added a new widget to any of the sidebar or footer, there wasn't anything I can edit or add on the widget. It disappeared. But I am able to edit the current widgets, but now I'm afraid to delete them, because I am unable to add new widgets.
See screenshot to see what I mean.
I tried both of the following:
1. Deactivate all plug-ins to see if the widgets are working properly.
2. Refresh wp-admin & wp-include folders from the freshest download.