Insecure password warning in Firefox

[P F Tinmore]

Frequently, but not always, I get a full screen warning about insecure passwords on USMB. The URL is USMB but the page is not. Usually I can hit the back button and hit my link again and it works. Sometimes I have to do that two or three time to get to the next page. If I click on security, I get this.

Insecure password warning in Firefox | Firefox Help

I have been using Firefox for USMB since 2009 and this is new.