iCloud Bookmarks
In iCloud, I have tried to use Firefox in the bookmarks set up options area. I have installed the Firefox add-on iCloud Bookmarks on Firefox. When I try to apply Firefox to iCloud, a window opens to tell me i require the add-on iCloud Bookmarks to be downloaded and added to Firefox. (It is already installed as an add-on in Firefox.) There is a spinning circle beside the Apply button. Why is this add-on not working? (I am using the most updated version of Firefox right now.) Thanks for your anticipated help with this problem.
Opaite Mbohovái (2)
I think this side can help you: https://support.apple.com/de-de/HT203519
The troubleshooting information you supplied doesn't show iCloud Bookmarks extension an installed extension, so it is possible that something went wrong installing this extension.
Note that we regularly see issues with the bookmarks reported caused by the iCloud Bookmarks extension.