A strange thing. I'm Win10, and i installed icloud app in Microsoft Store, then checked the ff in setting. All things looked good, but it couldn't sync my bookmarks.
Then I tried to install the app for Win7&8 (.exe). It asked me to download ff extension even I've got. It couldn't check the ff box in setting, but it works good. The bookmarks are synced.
Interesting😑

Sincroniza perfectamente con iCloud

Me gustaría que se pudiera sincronizar la navegación

Muito pesado e constates atualizações!