I love you all guys.
I just learnt that Firefox web page screen capture tools (any of them) can’t take web page screenshots higher than short 16-bit interger (32768) pixels. Crash crash crash. But I hope I am alone with my problem.
So, thanks for being so supportive… and it’s not fully rendered (over 250 of them), since after 3200 the image was cut. Excuse me if I am not willing to support your cause.