I block all third party cookies using Firefox and it worked fine on giant bomb until Firefox 65 came out, now the videos just won't play. Videos work fine in chrome with 3rd party cookies blocked.
I'm using Firefox 65.0. 64 bit on windows 10, I use no addons since I created a new Firefox profile for testing this. The only thing I changed is the content blocking setting to block all third party cookies. I tested with this video: https://www.giantbomb.com/shows/extra-life-2014-day-4-part-10/2970-13726/free-video
Here is a screenshot:
I can post more logs if needed but you should be able to reproduce this.