If you are not receiving a playback option on the Live display of your NVR, please use Internet Explorer 11.
The NVR's native way of control from a web browser is using a Microsoft's ActiveX plugin. As Firefox, Chrome and Safari do not support ActiveX, the job of the ActiveX control is emulated using Java and QuickTime. This method however does not give you 100% functionality as certain features require the ActiveX control, playback is one of them. However the backup process can still be run using non Internet Explorer based browsers.
Below are 2 screenshots showing the difference between a connection established with Internet Explorer 11 and Firefox.