This is to help others out in future. I had this problem for a while and couldn't find any other web page with a solution. I would go to the About Firefox dialog Click on Check for updates It would say "Firefox is up to date" Even though I knew version 41 was released and I had 39. (This also happened in the past with older versions. (I used to resort to updating manually with a fresh download.)) After digging, in about:config, I found the key app.update.url.override It had the value http://au4.moziila.org Note the double i - I suspect that some malware (removed a long time ago) inserted this value. I right-clicked and chose Reset. And now the update check works! Hope this helps someone else with the same issue.