My XFINITY TV Go "Watch Online" situation is this:
IE11: Slight chop/stutter on streaming video. Watchable for the most part as long as I don't maximize to full screen (which would be nice??) I have no problem streaming HD perfectly on virtually any other website. I also do some fairly GPU intesive video editing on this machine without a hitch.
Firefox: Error 422; can't play anything.
Firefox is my default browser, is a very recent install, and I would prefer to never use IE. I have a fast/clean running system: Windows 7 64-bit, 8GB RAM, dedicated GPU, i7 processor, SSD, fast internet connection (70-90 Mbps on average on wireless-AC router, which can support much more than available bandwidth, but have also tested w/ LAN cable..same result), no malware, no unnecessary processes running.
Yes... I clean cache regularly (via cccleaner, etc.) I have the latest versions of flash, java, etc. for both browsers. I have tried disabling anti-virus (MS security essentials, which I have never known to conflict with anything), and also tried disabling any plug-ins. Result is exactly the same.
I have also tried allowing looser privacy/security settings in Firefox, which thankfully wasn't the issue (tight security/privacy settings have never caused any issue in IE).
Hoping someone can reply with anything that may have worked for them, that I haven't already mentioned above.
Thanks!