Please try the suggestions in this article: [[Troubleshoot Firefox issues caused by malware]]

I thought this old scam was gone for good after a fix in Firefox some time back, but unfortunately it sounds as though it lives on. This is an old thread with some suggested approaches to escaping from such pages: [https://support.mozilla.org/questions/981475 WARNING FBI LOCKED BROWSER!!! ] It's also possible that this could be caused by something installed on your PC. Bad add-ons and other malware can sneak in with free software installers. Here's my suggested procedure for tracking down and cleaning up bad add-ons. Sorry for the length -- it's not as bad as it sounds: (1) Open the Windows '''Control Panel''', Uninstall a Program. After the list loads, click the "Installed on" column heading to group the infections, I mean, additions, by date. This can help in smoking out undisclosed bundle items that snuck in with some software you agreed to install. Take out as much trash as possible here. (2) Open Firefox's '''Add-ons page''' using either: * Ctrl+Shift+a * "3-bar" menu button (or Tools menu) > Add-ons In the left column, click '''Plugins'''. Set nonessential and unrecognized plugins to "Never Activate". In the left column, click '''Extensions'''. Then, if in doubt, disable (or Remove, if possible) unrecognized and unwanted extensions. Often a link will appear above at least one disabled extension to restart Firefox. You can complete your work on the tab and click one of the links as the last step. Any improvement? (3) You can search for remaining issues with the '''scanning/cleaning tools''' listed in our support article: [[Troubleshoot Firefox issues caused by malware]]. These on-demand scanners are free and take considerable time to run. If they finish quickly and especially if they require payment, you may have a serious infection. I suggest the specialized forums listed in the article in that case. Success?