I get notified by firefox when there is a newer version available. It is an option (selected by default I believe) in the advanced section of the Tools -> Opti

I get notified by firefox when there is a newer version available. It is an option (selected by default I believe) in the advanced section of the Tools -> Options dialog. It will even warn you if updating will disable any of your add-ons. I think your version of firefox may just have gone well past its use by date.