Verifique estes dois tópicos. Eu citei as seções relevantes para sua conveniência:
Olá,
Either set
media.mediasource.enabled
andmedia.mediasource.webm.enabled
to true in Firefox's about:config or install flash-player.Regards,
Antoine
Clear the cache and cookies only from websites that cause problems.
"Clear the Cache":
Firefox/Tools > Options > Advanced > Network > Cached Web Content: "Clear Now" "Remove Cookies" from sites causing problems:
Firefox/Tools > Options > Privacy > Cookies: "Show Cookies"
Outro método do mesmo segmento
Dear, Everyone who cares. I've had the same solution on and off for weeks, and I have just now found my solution. Try LOGGING OFF. Something in the account settings was doing it for me, but Logging off of my youtube / gmail account fixed this problem.
Spread the word.