Well Just found the latest 50x version of firefox on the system.
It works ok enough but I have noticed that there are some focus issues.
In the address bar, for example I type an address www.twitter.com/username.
When I delete one letter from the end of the address it maybe ok then nvda will start quoting the entire url out minus the deleted content.
If I left arrow I then get navigation toolbar address bar and search then the address so its losing focus, I can work round it by simple highlighting the particular section and killing it but ff likes to loose focus in some sites and forms and then if I push a key get it back again.
FF still works, but if this continues I am going to have to find out exactly how to turn off autoupdate and downgrade to 49.02 which still works.