Many people, including me, had a strange problem in the last few weeks that the xfire streams weren't working correctly and you couldn't watch them. I found a way how to fix this problem today and it's very simple. Just connect to a stream, click "Start Video" and wait till you can see the pause-button in the bottom left corner. Click pause and then click play again -> tada it works
tldr:
1. connect to a stream
2. start video
3. press pause, press play
4. watch it