This Firefox add-on displays a notification when a channel on Twitch, Youtube, Mixer or many more services goes live. Which channels are checked for being live is fully customizable.
There are more migration fixes to come (especially for those that no longer get status updates due to the migration only partially working). However I couldn't get further today and I wanted at least this to be out there. Enjoy your holidays, if you have any (and else just the weekend if this reaches you in time).