iCloud for Windows isn't the same unless it says iCloud for Firefox browser. Those are two different systems.

I notice in the description they say:

"The iCloud Passwords extension is compatible with macOS Sonoma or later. It is not available for Windows at this time." https://addons.mozilla.org/firefox/addon/icloud-passwords/

But if it worked in Edge, hmm, I wonder why it doesn't work in Firefox.

Does Apple support this extension in a way that would allow you to pose the question to them?

It occurs to me that the statement "The iCloud Passwords extension is compatible with macOS Sonoma or later - It is not available for Windows at this time", may refer specifically to the operation of Firefox on macOS, and excludes Windows. That could be because the Windows development is not yet complete or available. I hope so, and that it will arrive soon.

It does seem odd that the iCloud Passwords extension is available online and installable for Firefox on Windows, even though it doesn't work properly. This may be because the required developmental connections are not yet reliable. Time will tell.

I don't wish to provide the developers with an easy get-out, even though I fully understand that Mozilla development is non-commercial, and I for one am very grateful for their efforts, and I have personally provided modest financial rewards for doing just that.