Sleazy and annoying bulls**t: You hit your browser's back button or you go to close a tab to get rid of a web page and you get the arrogant an pushy message, "Are you sure you want to navigate away from this page?" And it doesn't matter what you click. It keeps you there or it even tries to install spyware or malware. So far my only way to deal with it is to kill the task with Ctrl+Alt+Delete or a nifty little utility called Task Killer. However, that brings Firefox completely down. What if I wanted to just kill the Firefox tab where that obnoxious site is? Is there any kind of Firefox plugin or other app that can do so? And anyone who uses that "are you sure you want to navigate away" script on their web page should be shot.
Are you running an old version of firefox I have no such problems i use Adblock Plus also avast 6 free antivirus it will not let you access such sites you would need to disable web-shields.
I've never had the issue of this pop up not going away. I agree with urie, keep your browser up to date and maybe recheck/rethink your protection.