Use the Firefox Settings menu to change camera and microphone permissions.
1. Click the menu button 
and select Settings.
2. Click Privacy & Security on the left.
3. Scroll down to the Permissions section.
4. Click the Setting button for the Microphone / Camera option.
Firefox displays the websites with saved Allow or Block permission.
5. Use the Allow/Block selector to change permission for the website. You can remove the site by selecting it from the list and clicking the Remove Website.
6. Select the Block new requests asking to access your microphone checkbox if you do not want to give any other sites access to your microphone.
7. Click the Save Changes button.