Here is a link to 201905
You have to remove 201908, install 201905 and reboot. Otherwise it’ll not do the job. If it still doesn’t work try uninstall, reboot, install, reboot.
BTW I have NOT downgraded firefox addon. It’s the latest as in my previous message (5.3.7)
PS. Do not expect all recent X related perks to work. Just thought I have to put out there “just in case”.