For streaming several channels (like ServusTV or WELT) on Fire HD tablets with Waipu.tv (app), whitelisting
imasdk.googleapis.com
seems to be necessary (otherwise channels won't load at all).
Disclaimer: With little to no knowledge on this domain I believe whitelisting this might introduce ad issues on other places (according to Commonly Whitelisted Domains - #41 by maxsteel or Werbung in Pro7 App auf FireTV).