[Suggestion] Blink support

[juanjgarcia]

Would be extra useful to have my prod server blink between default and block red in the hope it prevents me from doing something extra silly.

Happy to code it up if someone can provide a timing source within the Firefox API, never used it before.

Thanks for your hard work!

[ylecuyer]

I'm open to receive a PR for this feature. You don't need any special timing feature from firefox to get this
idea working.

You could add some metadata (like frequency and blink_active) to the environments objects and then use the common javascript setTimer with another call to setTimer inside, in the background.js to make the color blink.