Comodo Blocking port 80

Okay, weird one here. Sometimes when I start up my computer, I am connected to the internet (My IM services connect fine) but I can’t connect to any webpage (Aside from these forums) without disabling the Firewall, or restarting my computer until it works.

The web browser I use is Firefox, though the same thing happens with IE.

My antivirus is Avast, as people recommended that it worked well with comodo on these forums.

Okay, I pinned it down to being when Avast’s Webshield and Comodo’s firewall are running at the same time. It’s odd that it works sometimes and not others?