I visit a few sites that have a list of approved browsers and versions.
They actively block non-conforming access. Most are either financial sites or private sites.

Similarly, many sites code for IE access while ignoring other browsers.
I've found many sites that require IE to access/render their site correctly.
Fox News is one such site.

FF doesn't render the question on this page. Using IE there is a question with 4 answer selections and a Vote button.