Sorry if this is all obvious to you, but IMO it's better to be thorough with descriptions. Click on the Firefox tab on the upper left. In the window that appears, click on add-ons (on the right side of the window) and when the add-ons screen comes up you should see a list on the left that includes extensions and plug-ins. Click on extensions. On my computer, McAfee Script Scan for Firefox is listed in the extensions. If that also is the case for your machine, click on the disable tab to the right on the Script Scan bar. If all is right with the universe, that should solve the problem. Good luck.