What apple wont do! This extension is the best, and the dev also frequently updates it. If you have any issues the repository is on github. The repo's name is "icloud-passwords-firefox".

Sometimes there are issues, when apple updates the native iCloud Windows app, then the version number changes. If it breaks your extension just go into the file and change the name:

Exit Firefox
Edit c:\Program Files\Mozilla Firefox\FirefoxPwdMgrHostApp_manifest.json
In "path": I changed the iCloud version to 15.3.152.0: "C:\\Program Files\\WindowsApps\\AppleInc.iCloud_15.3.146.0_x64__nzyj5cx40ttqa\\iCloud\\iCloudPasswordsExtensionHelper.exe",

The repo's name is "icloud-passwords-firefox"