Rather than download Firefox updates many times for the same thing (for all the systems in our school) I prefer to download it once and then install it from a network share -- this reduces internet bandwidth utilization. But the standard Mozilla download sites, such as https://www.mozilla.org/en-US/firefox/all/, only have 43.0.1. I have checked the other "get Firefox now" links and they also only provide 43.0.1. It's been this way since 43.0.1 was available, i.e., it's stuck on 43.0.1!