Thank you for review.

Due to a change in the firefox specifications, it was no longer available.
I have fixed the problem in version 5.2.1.
Please check if it works with firefox 92 or higher.

[10/4 UPDATE]
It seems to be working fine on my end.
In order to determine the cause of the problem, could you please answer the following questions?
・Which checks are turned on?
・Which sites are not working?
・How would you like it to behave?