This bookmart script adds fbid of each post in facebook into the selector button on the top-right of each post.

fbidinject.js

(function(){
var elems = document.querySelectorAll('.uiUnifiedStory.uiStreamStory.genericStreamStory');
for(var i = 0; i < elems.length; ++i){
   var el = elems[i], a = el.querySelector('.uiSelectorButton.highlightSelectorButton');
   if(!a){continue;}
   a.href = JSON.parse(el.dataset.ft).fbid;
}
return false;
}())

/* minified and book-mark ready:

javascript:(function(){for(var b=document.querySelectorAll(".uiUnifiedStory.uiStreamStory.genericStreamStory"),a=0;a<b.length;++a){var c=b[a],d=c.querySelector(".uiSelectorButton.highlightSelectorButton");d&&(d.href=JSON.parse(c.dataset.ft).fbid)}return!1})();

*/