To unblock your microphone and webcam, do the following:
Click on the symbols (lock,microphone or webcam) in the addressbar of your browser.
The following Infobox appears:
Here you can unblock the microphone and webcam. Click on the X next to the text “Temporarily blocked”. This unblocks it.
Reload the page by pressing the “F5” key on the keyboard. Alternatively, you can press the “Reload page” button next to the address bar.