Recently I've been plagued by sites that hijack Javascript to not allow me to navigate away from the page (puts you in and endless loop of JS popup question boxes). Killing the browser doesnt work, nor does purging the chache. I run No Script in Firefox (on linux to boot) but it doesn't help. Sadly many of these links are from reddit et al.

Does anyone know what the technique is and of any good browser plugins to stop this?