customProtocolCheck seems to do nothing with FF (69 maybe more) on Linux (Ubuntu)

[StephaneG31]

My current UA : Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:69.0) Gecko/20100101 Firefox/69.0

I try to detect a custom protocol with the lib on Linux + FF.
Is it normal ?

[AsksaZgz]

Same in Windows 10 & Firefox 69

[git-kks]

Same with windows 10 and FF 98, did anyone fix the issue