I think normally exceptions are only added when you use the Allow button on the toolbar that tells you a popup was blocked. One possible culprit would be an extension. You can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. Either: * Ctrl+Shift+a (Mac: Command+Shift+a) * "3-bar" menu button (or Tools menu) > Add-ons In the left column, click Extensions. Then cast a critical eye over the list on the right side. Mozilla-installed extensions are hidden from this list, so everything you see here is your choice and your responsibility to enable, disable, or remove. If in doubt, disable. 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?