I purchased my MacIntosh laptop spring 2012 and downloaded Firefox. From time to time, automatically a window appears on my screen urging me to download the (latest) upgrade. When I click the "Download" button, a "wait" icon appears, which is a moving blue and white "barber's pole" , underneath which is written "Downloading Firefox Upgrade" (or something like that), but no matter how many hours I leave the download window on my desktop, nothing happens. Absolutely NO upgrade has been completed, and I am getting worried about this situation.