Firefox shows only blank pages - even about:config is just white

From one day to another Firefox shows only blank white pages:

I'v tried

• starting Firefox in --safe-mode
• starting Firefox with --ProfileManager and creating a new profile
• opening Developer Tools - but they did not show up
• removing ~/.mozilla
• reinstalled Firefox with sudo apt purge firefox && sudo apt install firefox

Nothing was working. Firefox even shows no error messages. Chromium still worked as expected.

When starting Firefox with strace I noticed by accident a library called libAppProtection.so. It is located at /usr/local/lib/AppProtection/:

$ ls /usr/local/lib/AppProtection/ -lah
total 188K
drwxr-xr-x 2 root root 4.0K Feb 23 17:35 .
drwxr-xr-x 6 root root 4.0K Jan  1 08:24 ..
lrwxrwxrwx 1 root root   56 Feb 23 17:35 libAppProtection.so -> /usr/local/lib/AppProtection   /libAppProtection.so.1.6.7.3
-rwxr-xr-x 1 root root 175K Jan  1 08:24 libAppProtection.so.1.6.7.3
-rw-r--r-- 1 root root   44 Jan  1 08:24 .XInputEventIDs
$

After renaming the folder I got a lot of error messages - on every command I execute, even in the shell - but Firefox worked again as expected.

It turned out that libAppProtection.so was part of the Citrix Workspace App SDK 2101 which I installed some days ago. It needs a restart of Firefox to make problems. So I removed the current installation with

$ sudo apt purge icaclient
[...]
$

and downloaded the workspace app and installed it without the app protection: