There is nothing more irritating to a visitor than a site that appears to be trying to control them, either by forcing them down particular paths, of by disabling features of their browser interface.
Here are a couple of examples of the sort of thing I am talking about:
These techniques can decrease accessibility as they go against users expectations about how the web works. I expect to be able to click the back button in my browser to move back to the last page viewed; and I don’t expect my back button to suddenly stop working.
Trying to control the visitors to your site is a bad thing; not only can it make your website less accessible it can also make you seem less credible as an organisation; that’s what happens when things on your site don’t work as expected.