Here another similar case
For me It’s the same OS and firefox used with old Kantu.
I do not have any recent update of OS it’s the same OS used with old Kantu and Xmodules.
If others users have the same bugs there are a problem in new firefox kantu addons 5.2.3 and xmoduiles 08-2019
Downgrade Kantu and xmodules working all, it’s the latest update of firefox kantu addons and xmodules.
Thanks