Sometimes when you download items and click Agree, you are inadvertently allowing certain applications to install malware onto your computer. 

To check your Browser Extension Preferences and remove extensions on Firefox , please follow the steps below: 

1. Open Firefox , click on Firefox , and select Preferences. 
   
    
2. Click on the Privacy & Security tab, scroll down to Permissions, and tick Block Pop-up Windows. 
   
3. Some web sits may require Pop-Ups. To allow selected websites the ability to display Pop-Ups you can add the website to your list of site exceptions. To do this, click on Exceptions. 
   
   
    
4. You will then need to enter the chosen website address and press Allow. 
   
    
5. Press Save Changes. This website will now be able to display Pop-Ups whilst stopping other websites.