Firefox Update Popup

Mozilla support articles frequently state that Firefox does not use popups for browser updates. However, I periodically receive popups from the toolbar stating that Firefox couldn't update automatically. The attached picture is an example from the web but looks just like the popups I receive. The issue typically either resolves itself or I download from the Firefox website and reinstall. In a rush/moment of weakness, I recently clicked the link in the popup. It took me directly to the Firefox website where I regrettably downloaded and updated the browser. I've since run multiple Norton and Malwarebytes scans, which have found no issues. It may be a difference in the definition of popups (from the toolbar vs within a browser page)... Is this a legitimate update message from Firefox? If it is not, are there any other steps I should take (e.g., reinstall Firefox)? I appreciate your help!