Is that not sent from the site to let you know that Microphone is on or is available ? Would have to send the URL to look at it if is something do not have to log into. If you use the Microphone then by disabling it for this site would not be useful.

Can go to the Control Far Left of Address Bar (Show Site Information) Click the Click the Arrow and then More Information then Permissions. Untick what you think.

Copy/Paste about:preferences#privacy to the Address Bar then Enter. Down to Permissions and Block what you want and sites that have populated this. Will not do away with the Icon. As said it is sent by the Site I think.

Please let us know if this solved your issue or if need further assistance.

It is for discord through the discord website. I shouldn't have to have this button displayed because I am using discord. If I use discord on Google Chrome, I don't get this icon.

What happens if you disable the mike on these pages via "Page Info -> Permissions" in case you aren't using it?

Discord is a voice chat service, I want to use my mic with it. :(

Support volunteers can experiment with the feature using this demo site: http://mdn.github.io/voice-change-o-matic/

It seems as long as the mic is live on any website, that pair of buttons stays on top. You can drag it left/right (click to make it stick in the new location), but I don't see a way to hide it.

It probably has a Windows attribute set to make it stay on top, so likely a Windows utility that can modify that attribute could demote or hide it if it's that intolerable.