403 forbidden

Cant access some sites, even though others on my network can. Is comodo firewall responsible for this, I have it installed with custom and safe mode. I get the 403 message while surfing.

If the firewall was blocking you would get a server not found message.
403 is a server message. You do connect to the site, but the server will not let you view that specific folder in the website tree.
Since you say others can connect, perhaps the website restricts access based on some criteria. maybe your OS or browser.