You want to install Marketplace apps for your Firefox Desktop.
You are working with IGEL Linux 5.06.100 and Firefox 31 or higher.
When you install such an app, a progress bar appears and is running endlessly, but the selected app is not being installed.
This is intended by IGEL because it may cause problems. The reason is that the partition holding all Firefox profiles is only 50 MB large.
If you nevertheless need to install a Webapp, switch the respective registry key:
IGEL's Terms & Conditions apply.