If you have the microphone blocked by default and need to enable it, just follow these basic instructions (images made with Chrome but should work for most browsers):
1. Click on the padlock on the top left corner of your browser. Maybe instead of a padlock, it appears an image of a white paper, it does not matter.
2. This drop down menu will show up. Search for the microphone option and then select 'always allow for this site' option.