It was loading the log-in pop up UNDER the main window instead of on top of it.

Same issue but the root cause is not a hidden pop up. When I browse I get the pop up for master password I enter it but pop up keeps coming back like not the right one. I know it's not the case : I'm logged in using the PW here. I tried restart PC, switch to maintenance mode, cache clearing, nothing changes. Then disconnecting / reconnecting that made things worse : possible to disconnect impossible to reconnect. Last, impossible de reset the password from FF menus. you could access and get the pop up window but the "enter" option was "greyed", only the "cancel" option to go back active.

Looks like the last update just F... up the links to the server.

You can can inspect the current login state and login and logout and change the Primary Password via the Security Device Manager.

• Settings -> Privacy & Security
  Security -> Certificates -> Security Devices

In the left panel select "Software Security Device". You can find "Log In" and "Log Out" and "Change Password" in the very right panel. You may have to Zoom out the page or go full screen to make this right panel visible.