My microphone isn't picking up my voice
I found the solution, Isabella-Vermont! I had the same issue and then I made 3 things to fix it: 1) Duolingo Settings - Microphone ON: Click or hover on the upper right corner of Duolingo website and go to Settings and make sure the Microphone is set to ON. 2) Make sure the microphone is plugged into the computer and then do the Flash microphone test at http://msuconfuciusinstitute.org/scheduler/mictest.php to check if the microphone is working in your Firefox browser. 3) As user iox said, Go to go to this special Adobe page: http://www.macromedia.com/support/documentation/es/flashplayer/help/settings_manager06.html , and there set duolingo as "Always allow". This is because the duoling recorder doesn't ask you for permission, and so it can't access the mic. Once you add duolingo as a trusted site that can access your mic, recording works perfectly.
I tried all the things written here, and THEN, in order for it to work on chrome, I started a new lesson and when the first microphone exercise came up -there was a light grey banner appearing (pay attention, it is very discreet) at the uphand field, asking me whether I allow duolingo to use my microphone. I clicked yes and after that it has worked beautifully!