Video doesn't work on Firefox when it's already open elsewhere

[fsih]

Expected Behavior

When webcam access is allowed, video motion extension should show video in background of stage

Actual Behavior

video not working

Steps to Reproduce

(0. Open webcam from another tab of firefox, or another app, or chrome)

1. Add video extension
2. Say yes on permissions
   Video doesn't appear and this error is in the console:
   gui error Unhandled video io device error
   MediaStreamError { name: "NotReadableError", message: "Failed to allocate videosource", constraint: "", stack: "" }

If you access the webcam from a different app on the computer, then try again in Firefox, then the video starts working.

Operating System and Browser

Firefox Windows

[paulkaplan]

Yeah, we should handle this error and show a helpful message in this case.