After installing swfdec and swfdec-mozilla, but before I added my user to the audio group, I started firefox and tried playing a youtube video. The browser would immediately close. I believe this crash is caused because swfdec expected access to the audio device to be granted, and it crashed when it was denied. After adding my user to the audio group, the videos successfully played.
I cannot reproduce it with the current code. It may depend in whether libmad is used. It's no longer used by default. Make sure to install gstreamer-plugins-bad and gstreamer-plugins-ugly for sound formats with patent and other problems.
This should be fixed since 0.5.3, indeed.
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