The problem is basically that i can only have one thing reproducing sound at a time, for example, only one youtube video can reproduce sound while there are variuos other playing; but it is not only a browser thing, if, for example amarok is playing music, the browser will stop outputting sound.
I do believe that the problem started when i followed the guide of WineHQ to use wine with ALSA (WineAndPulseaudio - The Official Wine Wiki), because my wine could not reproduce sound if i did not execute it that way (there is a small posibility that the problem started before, my memory is a little skewed, but i am pretty sure that it started then).
Any way, that is the only multimedia modification that i have done.
Thanks beforehand!