Fedora 19, Music in Youtube

[Andreas Aßmann]

I installed Fedora 19 on two laptops (one 32 bit and the other 64 bit). 
In the beginning, after the initial installation of Fedora 19, I could 
listen to music videos on Youtube on both of the two laptops without any 
problem. But at a certain moment, I could not hear anything any more (in 
the video, there is now a little "Andrew cross" on the right side of the 
loudspeaker symbol).

Does anyone of you have an explanation or even a solution for this 
problem? Is there an incompatibility with updates installed AFTER the 
initial installation?

Thanks so lot. Greetings

Andrew