Firefox recommends that you don't enter your password

[Dave Howorth]

I just updated an Ubuntu 12.04 machine and the update included Firefox 45.

The first thing I then tried to do was to log in to our shared systems 
at work, and Firefox said:

"Firefox recommends that you don't enter your password,
credit card and other personal information on this
website"

With a button labelled "Don't Trust This Website" alongside.

Clearly that's not an option for a $work system, so I'd like to 
understand why it is making that suggestion.

There doesn't seem to be anything in the help or on the intertubes.

All ideas gratefully received.

Cheers, Dave