Ingress Community Forum: cannot log in (Firefox, Windows)

in Report a Bug
When I try to log in to the Ingress Community Forum, I get the error message "Something went wrong with your sign-in process. Please check your pop-up blocker."
OS: Windows 10
Firefox 91.3.0esr
The problem started a couple of weeks ago. Browser settings are managed by my employer, I have no control over them. The pop-up browser window for the Google sign-in opens correctly.
No login problem with Edge browser.
The Ingress Community Forum does not use pop-ups, so why would the settings of the pop-up blocker cause problems for the sign-in process?
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