Do the popups happen on all sites? If so, it could be spyware. # Ensure you don't have any Firefox extensions that may be affecting the behavior of websites. See [[Troubleshooting extensions and themes]] for instructions on testing whether extensions are causing a problem. # See [[Is my Firefox problem a result of malware]] to determine whether spyware is likely causing the issue If spyware is at fault, a number of popular freeware malware scanners can be used. Some examples are: * [http://www.malwarebytes.org] (Malwarebytes; free version works to remove spyware, but is limited in some features) * [http://www.microsoft.com/security/malwareremove/default.aspx] (Microsoft Malicious Software Removal Tool) * [http://www.safer-networking.org] (Spybot Search & Destroy)