I don't have that extension, I do have Comcast, and I don't see injected Comcast content. Either uBO or another blocker (belt and suspenders) is blocking that, or they don't do it in my region, or my block, or whatever.

They only inject when you're on "xfinitywifi" networks and if you've pirated something and they want to inform you that you've been caught, iirc.

Not true. They've been injecting ads to my android phone which is served by a wireless device I own. And I haven't pirated anything. I had to switch to Firefox with ublock to fix it.