Sounds like an add-on may be doing that. Where does the checkmark appear? If you haven't reviewed your extensions recently, you may want to take a look and see whether anything unexpected has crept in, or whether you want to adjust how they work. You can do that on the Add-ons page. Either: * Ctrl+Shift+a (Mac: Command+Shift+a) * "3-bar" menu button (or Tools menu) > Add-ons * type or paste '''about:addons''' in the address bar and press Enter/Return In the left column of the Add-ons page, click Extensions. Then cast a critical eye over the list on the right side. Any extensions that Firefox installs on its own are hidden from this page, so everything listed here is your choice (and your responsibility) to manage. Anything you don't recognize or don't need here? If in doubt, disable. If you have any that relate to security or safety, perhaps that's the culprit. You can use the More links for more information. Often a link will appear above at least one disabled extension to restart Firefox before the change takes effect. You can complete your work on the tab and click one of the links as the last step. Any improvement?