I can not install Firefox 9. He asks an additional download. This download is never concluded, after a while the download progress dialog disappears, the installation dialog is activated again and if I choose to install it again asks to download.

Try to deactivate your antivirus and your firewall (just during download) because they can take too much time to check the download (or they can just reject them) and the Liberkey installer could think there are an issue downloading the binaries (so it ask you again and again to download binaries)

I disabled Antivirus and it worked. Thank you!