How do I access the flash microphone settings?
I am using Firefox on Ubuntu and I have tested that the microphone works within flash on other sites, but on duolingo I don't get the flash settings popup asking for permission to access the camera/microphone and when I right click in the flash area the settings option is greyed out so I can't manually set it either.
I think it has to do with the embedded Flash element being too small to have enough room for requesting camera/microphone access permissions. Use this to grant access to duolingo.com: http://www.macromedia.com/support/documentation/en/flashplayer/help/settings_manager06.html
No need to ditch Firefox, it's a great browser. :-P
Have you tried reinstalling the flash plugin? On Ubuntu, this should do that:
sudo apt-get --reinstall install flashplugin-installer
Also, try another browser, perhaps Chrome. There could be a firefox add-on that is conflicting with the flash plugin.