Sometimes the toolbar layout gets gummed up but before diving into that, have you checked these issues: (1) Overflow When there are too many buttons, new ones are added to the overflow menu at the end of the bar (just before the menu button). Do you have an overflow list? If you need to move a button from overflow back to the main part of the bar, call up the Customize panel: [[Customize Firefox controls, buttons and toolbars]]. (2) Not on any bar Check the Customize panel to see whether the button is available to drag to the bar from the box there: [[Customize Firefox controls, buttons and toolbars]]. (3) Blocked by private mode Extensions don't automatically have permission to run in private windows. That needs to be allowed either in the install confirmation dialog, or on the Add-ons page, Details panel. More info: [[Extensions in Private Browsing]]. Any progress so far?