Hmm, was it a drop-down from the menu button? Usually that appears a few times a day and doesn't affect tabs. But after an extension installs in the background, a tab may require restarting Firefox. Is that the one you're seeing? If necessary, you can manually trigger an update and/or restart Firefox in mid-update from the About Firefox dialog. Either: * menu button > Help > About Firefox * (optional menu bar or Alt+H) Help > About Firefox