Firefox 39 is currently in Beta state and will be the next release (probably next Tuesday June 30). *https://www.google.com/calendar/embed?src=bW96aWxsYS5jb21fZGJxODRhbnI5aTh0Y25taGFiYXRzdHY1Y29AZ3JvdXAuY2FsZW5kYXIuZ29vZ2xlLmNvbQ So you can ignore this pop-up. You can check the update channel in "Help > About" and on the about:support page to make sure you are on the Release update channel. If you are not on the release channel then you should install the current release (38.0.5). You can find the full version of the current current Firefox release (38.0.5) in all languages and all operating systems here: *https://www.mozilla.org/en-US/firefox/all/