As many others have said, it doesn't work. Mozilla should probably just remove the extension until Apple decides to maintain it.

If you enable Firefox sync in the iCloud settings it directs you to download the extension which you have already downloaded. This is a straight up bug in iCloud but I don't have high hopes that it will get fixed given the generally abysmal quality of iCloud on Windows.

Broken, and has been for years on Windows 8.1 and 10. It will synchronize once and then completely breaks and never updates again (iCloud forgets the addon is installed) Have to wipe all bookmarks, delete the addon, and start all over in order to get it to synchronize one more time. Not worth the effort.

Edit: Update 2022 - Addon still constantly breaking. Extremely lame. Seems to stop working if I don't synchronize every week. Really hard to safely reset without wiping out all bookmarks or duplicating everything.

用不了咯！

Não funciona!

Used to work perfectly. Now, even with an icloud update this morning to 7.20, the extension no longer works. Just keeps telling me to install the extension (which is already installed) and won't allow the sync bookmarks box to be checked and applied. Tried removing and reinstalling the extension and it still won't work. Spoke with AppleCare, and they said it's not on their end. Very sad, as I've happily used this, and it worked perfectly, until about a month ago.

iCloud for Windows erkennt die Installation des addon nicht. Daher keine Lesezeichen Synchonisation möglich.

does not work

No hay manera de que se sincroniza con iCloud, no admite "aplicar" en "ajustes de iCloud" (Windows 10) después de descargar la extensión.

Used to work, now it will not work at all. When you select in iCloud settings to sync with Firefox, the ICloud app tells you that you must install the iCloud extension in Firefox, which I already have from before, and then it never accepts or keeps the box checked in the iCloud app. Have tried removing the Firefox extension and re-adding to no avail.

Не работает с браузерами Mozilla и Chrome (iCloud for Windows)

Needs updating.

Keeps prompting me to download this extension, which I've done multiple times (also, I've reinstalled Firefox). Bookmarks do not sync.

Impossivel instalar. Impossible to install.
Instalação interrompida porque a extensão parece estar corrompida.

me duplica y triplica los marcadores, funciona en general bastante mal

Confusing.