Works fine, but ONLY if FF is not set to "https only". And no, it does not help to define exceptions for https in FF. What a pity.

Still works pretty well.
For those, who say "it stopped working suddenly": just re-enter your api key. That's it!
Just one thing i would like to change: the off-time which is pre-set to 10 minutees should be variable. I would like to set my standard off-time to 2 mins, so i don't have to change it every time i have to set my pihole off