Do you think it could be a Firefox add-on? Ad blockers are typically '''extensions.''' 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. All extensions are optional. 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? ---- Note: If you are using your email site in a private window, check for possible effects of Tracking Protection. This article has more information on how to spot whether Tracking Protection has blocked some content in the page, how to make an exception, and how to turn off the feature if you find it is more trouble than it is worth for your needs: [[Tracking Protection in Private Browsing]].