This addon i made by new addon's API promoted by Mozilla (to please Google, i think) - WebExtension (at begining - a Chrome extensions API). And it was made by Mozilla's guides on MDN,
On my Firefox 50 it works well, but after guys from Mozilla broke something - and now it does not work properly.
When i have enought time to understand what this brave guys did in such a way that this even broke what they themselves described in guides - i will fix it.
But at this moment my Firefox still has version 50, because at next versions they killed XUL and XPCOM :(
P.S. I fixed my addon. Now version 1.57 works fine in all late FF. Enjoy!