When you first visit a website, you might get a prompt on the left side of the URL bar, which says the website wants to access your microphone or webcam. You must hit allow in order to use them. See the picture below for an example.

If you did not hit “Allow”, or have default settings to block access, you may see error messages like the one below, or the website may not show any webcams as available.

To fix this, click the icon with a small red x at the right side of the URL bar, and then change the checkbox to “Allow”, hit done, and refresh the page.