On Mac, the most common reason to get this is Spigot or Conduit add-ons. You can check for those on the Add-ons page, either: * Command+Shift+a * "3-bar" menu button (or Tools menu) > Add-ons 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? Note that such add-ons may have been part of a bundle with something else and may be re-injected into Firefox if the bundle installer is not removed from your system.