Thank you for reporting the bug.

I checked it in my environment (mac os bigsur and Windows10: FireFox90.0.2 (64-bit)), but the problem does not reproduce.

Can you tell us about your environment?
I will create the same environment as you and reproduce the defect.

If you don't mind, can you tell me what other add-ons you are using? (Check if it interferes with other add-ons.)

thank you.