>>For a while, I get blank page (URL https://www.levelextreme.com/ViewPageGenericWorker.aspx) after the first login in Firefox. Subsequent login works.
>
>I cannot simulate this. I have Firefox 43.0.4.
>
>Can you give me step by step a simulation pattern?

Had this in the last 4 days:
was logged in in FF,
looked something up on tablet without logging out on PC
back on PC my session was removed by second log in
new log in -> blank page
second log in works as expected

you probably can find it in the logs, not much other logins as usually I stay logged in