Backoffice login process freezes with loader animation and oauth_complete Url

Questions
1

When I try to log into the backend, the process freezes with a three dot loader animation. In the browser address line there is a URL “…umbraco/oauth_complete?code=r3okjNnaNxSvBtgEkFgTDSGt9yXb_FR7rRG_HzP5EmI&state=tqjZQWFhqw&iss=https%3A%…”
It seems that some kind of authentification does not happen and because of that I am not beeing redirected to the backoffice correctly. But obviously the login process succeeded somehow, because when I re-enter the umbraco backoffice url manually in the browser address the backoffice shows up and I am logged in as a user.

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.
3

Just want to note that I use Firefox daily and have many different backoffices that I log in to, never seen this problem.

Maybe one of your browser extensions is causing this?

4

I have reproduced it on two diferent computers both with the latest Firefox 138.0.1 - no Firefox plugins. Umbraco Version 15.4.1