For more information on detecting a misleading pop-up, see Pop-up blocker settings, exceptions and troubleshooting.
Make sure you install add-ons from Mozilla's add-on website and you uncheck unwanted programs in software wizards. Usually, these programs gather information on your browsing behavior that serve only the people who designed them and interfere with Firefox. Some unwanted programs also come bundled in software packages.
Make sure you are using the latest version of all software you use, either by enabling the software's automatic update feature, if available, or by checking for updates from the software provider and by using the Windows Update feature. Keep your operating system and other software updated: Installation of malicious software usually takes advantage of known security vulnerabilities in other programs, which may have been patched in later versions.There are simple rules to follow in order to prevent malware from being installed on your computer: How do I prevent malware from being installed? For more information, see Identify problems caused by third-party modules in Firefox for Windows. These modules are displayed on the Firefox about:third-party page. The malware may have loaded modules into Firefox.
For more information on customizing Firefox, see Remove a toolbar that has taken over your Firefox search or home page and How to remove the Babylon toolbar, home page and search engine.
For more information on blocking popups, see Pop-up blocker settings, exceptions and troubleshooting.
Symptoms are various and depend on the malware, but if you have one or several of these behaviors, you may have malware installed on your computer. How do I know that my Firefox problem is a result of malware? 2 How do I prevent malware from being installed?.1 How do I know that my Firefox problem is a result of malware?.