I'm surprised to not see more messages in here about this since a simple google search show hundreds of people with the same problem. FIOS being super slow with YouTube, while other websites and streaming services are fine, I have a 50 mb plan, and speed test of every single place show that speed, streaming video from VIMEO, Netflix, and every other HD streaming I tested works wonderfully, except YouTube, which I can't even stream a simple SD video.
Calling to support is sort of useless because the only thing one get is a .. Please reboot your router... I'll send you a "signal" from here to fix it... Have you reboot your computer? Do you have a firewall? Sound like you are reading a manual...
Come on! Stop treating us a dumb clients, I have 5 computers at home, 2 are laptops, and when I go to my office, 8 miles from home, different provider, YouTube HD videos fully load in matter of seconds, I save the link and try home, and watch a 5 minutes video takes about 20 minutes..
As unfortunate as it is, I put up with those routine bi-monthly week long slow-downs as well. For the most part it never seems to be an issue with Verizon as there's always another ISP seeing the same thing (and the last one, it wasn't just Verizon; Cox saw the same problems and even more distant, European ISPs had the same problems). While I know it would be nice for Verizon to just come out and say it's YouTube's problem which it generally is, they really don't support the site besides making the peering agreements to connect to Google's network. The fact that Google has a CDN for that site which takes you to different servers depending on ISP and location (and even DNS Servers), doesn't really help the matter out either which is why tech support won't exactly be able to give you a clear answer.