- Why would you open your firewall to the safe LAN inside?
I can only see opening your firewall so [malicious] people overseas can control your TV.*
*If you're under the impression that opening ports makes packets "go to the TV faster" or without "restrictions" - the firewall is intelligent enough already to Establish/Relate traffic. Firewalls have done that for about 15+ years now. No need to open ports on a default OpenWrt firewall setup since the TV on the allowed LAN will initiate the request.
FYI, if successful, you might also block a portion of the Google CDN not ad-related (ads in some cases seem to be on servers with other content), YMMV.