Whilst I wouldn’t recommend this as a long term solution (but better than completely disabling the web shield), what happens if you just disabled the https scanning in the web shield settings ?

We are seeing some topics like this for those using XP and Vista, though I don’t experience it on my XP system (in my signature below my posts).
What browser are you using ?
Do you also have the avast browser security add-on (AOS) installed ?

I don’t use Comodo firewall, so I have no experience of its interaction with avast, especially if you have Defence+ or its AV enabled ?