Even if you add the app on iCloud still won't back up your Bookmarks all you get is a pop up window telling you to download the app, but you already did. So it's useless.

Crashes every time and I am not going to the abusive apple site to try to find an answer.

I hate this and I can't figure out how to cancel/reverse it. Help me please

Exactly Same!!!!!
Windows 10 Pro (64bit) + Firefox 71 (64bit)

"Will not work on Windows 10 64bit. Does not recognize that the Add-On is installed, even though it is. As about 350 others have said, this is worthless. Keeps prompting me to download and install a file. Takes you into an endless loop of BS. I stopped trying. How is it possible that they have not fixed this issue. Not like Windows 10 and Firefox are new!" -Michael Lynch

Same!!!!!

"Will not work on Windows 10 64bit. Does not recognize that the Add-On is installed, even though it is. As about 350 others have said, this is worthless. Keeps prompting me to download and install a file. Takes you into an endless loop of BS. I stopped trying. How is it possible that they have not fixed this issue. Not like Windows 10 and Firefox are new!" -Michael Lynch

Same!!!!!

火狐浏览器已安装icloud扩展，仍不停的提示下载安装icloud扩展。

Will not work on Windows 10 64bit. Does not recognize that the Add-On is installed, even though it is. As about 350 others have said, this is worthless. Keeps prompting me to download and install a file. Takes you into an endless loop of BS. I stopped trying. How is it possible that they have not fixed this issue. Not like Windows 10 and Firefox are new!

Extension keeps prompting me to download/install in Firefox, even though it's already installed. Unable to activate the Extension despite repeated attempts.

FAIL. Doesn't work on Windows 10 64-bit. I tried to save my Firefox bookmarks to my iCloud account but was unable to. I am repeatedly prompted to download the iCloud Bookmarks extension for Firefox even though it has already been downloaded. Waste of time.

No funciona, al intentar habilitar la opción en la aplicación de iCloud para Windows siempre manda instalar la extensión sin hacer nada más.

iCloud fordert auf, die Lesezeichenerweiterung zu installieren => ist sie aber bereits

Stopped working.

Doesn't work. iCloud client gives a prompt to install the extension, but it's been already installed

Installation aborted because the add-on appears to be corrupt.

本来用作电脑 Chrome / Firefox 和手机、平板 Safari 书签同步非常方便，直到有一天我打开了 Chrome，眼睁睁地看着我的整行文件夹和书签一个个消失，心中崩腾而过无数只草泥马，没办法赶快打开 Firefox 想着备份下来，万万没想到噩梦重演，破扩展立马同步过去了，Firefox 里的书签也一个个消失，还有删除动画，你们能想象我当时的心情吗！！！还好 Firefox 有每日自动备份，重新恢复后正常了。然而你以为就这么简单吗？隔了一天打开 Firefox，书签自动复制了两遍，花了好久才把重复的几百条删干净，没想到这回同步一点也不及时了，Chrome 里又把删掉的给我同步回来了，Firefox 立马又同步上了，这回是三遍书签，简直是噩梦！立马卸载 iCloud 删扩展，再您妈的见！

funktioniert nicht mehr!

iCloud-Lesezeichen kann unter Windows 10, 64 bit auf FIREFOX V 70.0.1 nicht installiert werden.
Meldung "Laden Sie Firefox herunter".
Add-On cannot be installed since Firefox Installation can not be detected !