Great - the author has created a working addon (after all, it is not a matter of course) as he described it. I can reactivate my right clicks (even if they have already been disabled by the website) as intended.

尼玛，牛逼，网课考试神器啊233

Vielen Dank!

Perfetta

work like charm!

excellent

Not working at
https://letters.gov.spb.ru/reception/form/
("Содержание обращения" field)

Maybe some kind of key press emulation is needed in such cases?