The reason the recording button is missing is that you have a toolbar in the browser that is pushing the buttons down out of view. There are two ways to solve this:
1) Hit the F11 key on your keyboard to go to full screen, then hit the add audio video button again. This will open a window without toolbars so everything will show up.
2) Disable the toolbar in your browser. You may need to go into the add ons or extensions area in your browser settings to do this.