Since the latest update, Firefox will not play sound on websites while sandboxed.
I have tried it without the sandbox and the sound works fine. I have deleted the contents of the sandbox again and again, and nothing changes.
Additional System Details
- Shockwave Flash 26.0 r0
- User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:56.0) Gecko/20100101 Firefox/56.0