I like the idea since it may be really frustrating when people disable comments under their writeups.<p>Some feedback: your landing page discouraged me from using this. Why do I need to sign up? Especially when you write about being anonymous. I think that perfect landing page would involve a brief information about what is it, and a big-ass "add to chrome" button, and that's it. You can explain the rest of it once I'm in, right now there is a lot of things going on and it's hard to realize what I need to do - should I read the description? But then something moves on the right side, oh and then the point #1 becomes inactive.
Have you seen <a href="https://hypothes.is/" rel="nofollow">https://hypothes.is/</a>? Not to discourage you, I'm just seeing because maybe it is exactly the same thing you are building here, and that should be good, right?