Its a common problem with pulse audio that it plays audio on just one flash application and doesn’t output any audio to other flash or applications.
That is not a problem actually, it is because when you install alsa it doesn’t install all components by default rather it just installs the necessary components. To support audio on multiple applications you need to install pulseaudio configuration tool and alsa plugin for pulseaudio-alsa.
$ sudo pacman -S pavucontrol $ sudo pacman -S pulseaudio-alsa
that will resolve your problem
keep enjoying 🙂