Backoffice login process freezes with loader animation and oauth_complete Url

Questions
2

Here is an update:

  1. I cannot reproduce this error with Edge.
  2. With Firefox I can log into the backoffice once with browser window and freshly cleared browser cache. Then when I log out and try to re-login again (with the same user or another), the process freezes in the manner described above. When I clear the brower cache (in Firefox it is called “temporary cached files and pages”) again, the login works for one more time.
    So it has to do with the firefox unfortunately.