Comment 8 for bug 1521789

I ran into this myself. From the above it looks like you use apparmor too so it's probably the same problem I had---Firefox uses GStreamer and 15.10 shipped a new version which changes the path. Try running your browser unconfined to see if it fixes the problem and then use complain mode to identify which files you need to give it access to. For me it was these:

/usr/lib/x86_64-linux-gnu/gstreamer1.0/gstreamer-1.0/gst-plugin-scanner
/home/myuser/.cache/gstreamer-1.0/registry.x86_64.bin