This purple capsule icon appears in the upper left-hand corner of my Firefox browser when I share a tab using Zoom or Google meet. It does not go away when I stop sharing my screen, or if I quit Zoom. If I'm using two displays, sometimes it sticks on one screen when I move my Firefox window and hovers over every window in any app. The only way I can make it disappear is to quit and restart Firefox, which isn't practical. I can't find any setting in the Mac Control Panel or in Firefox to turn this off (Reddit is split on if this is a Firefox problem or a MacOS problem).