In order to play RTSP streams with Firefox, start Firefox and open this address:
Click the 'I'll be careful, I promise!' button.
Make a right-click on any location on the page and select New > Boolean.
In the pop up window, submit 'network.protocol-handler.expose.rtsp' and click OK.
In the next pop up window, select 'false' and click OK.
When clicking an RTSP link, Firefox will ask you now to choose which application you want to use. Select any media player of your choice and validate it.