Well, I tried as you suggested, small drop of part B on light. It is late evening, so it is tungsten light. I made digital photo of result after approx. 5 minutes. There was no more change in color, only in smell around :-). So fomabrom doesn't interact .... I don't understand yet what is principle, but I can see results.
All papers FB: foma, foma, foma, ilford.