This occurred when opening a web page? Some sites are malicious or hacked, so that might have been the cause of the popups. If you did not download anything -- you can use Ctrl+J to see recent downloads -- or give them any information, or connect them to any of your logged in services (like Google, Outlook, Facebook, etc.), or install any new add-ons from them, then ''probably'' all is well. If you want a second opinion, the following article recommends cleaning tools other Firefox users have found helpful: [[Troubleshoot Firefox issues caused by malware]]. For future reference, Ctrl+W will close the current tab. It should work even on attack pages where they make it hard to close out with the mouse.