The Web shield works regardless of the browser you are using. The webshield does not alter the page
content (unless a threat is found of course) nor does it interact with the browser GUI. If it is on or off can
be managed/seen on the preferences page in the Avast GUI.
You are probably referring to the AOS browser extension, that provides some additional features like
page ratings. The AOS extensions/browser plugins must be installed separately which can be done from
the "Tools" page in the Avast GUI.