Выделение элемента курсором

function getFiltersForElement(element, callback)
{
  let src = element.getAttribute("src");
  browser.runtime.sendMessage({
    type: "composer.getFilters",
    tagName: element.localName,
    id: element.id,
    src: src && src.length <= 1000 ? src : null,
    style: element.getAttribute("style"),
    classes: Array.prototype.slice.call(element.classList),
    urls: getURLsFromElement(element),
    mediatype: typeMap.get(element.localName),
    baseURL: document.location.href
  },
  response =>
  {
    callback(response.filters, response.selectors);
  });
}

function startPickingElement()
{
  currentlyPickingElement = true;
 
  // Add (currently invisible) overlays for blockable elements that don't emit
  // mouse events, so that they can still be selected.
  /*Array.prototype.forEach.call(
    document.querySelectorAll("object,embed,iframe,frame"),
    element =>
    {
      getFiltersForElement(element, filters =>
      {
        if (filters.length > 0)
          addElementOverlay(element);
      });
    }
  );*/
 
  document.addEventListener("mousedown", stopEventPropagation, true);
  document.addEventListener("mouseup", stopEventPropagation, true);
  document.addEventListener("mouseenter", stopEventPropagation, true);
  document.addEventListener("mouseleave", stopEventPropagation, true);
  document.addEventListener("mouseover", mouseOver, true);
  document.addEventListener("mouseout", mouseOut, true);
  document.addEventListener("click", elementPicked, true);
  document.addEventListener("contextmenu", elementPicked, true);
  document.addEventListener("keydown", keyDown, true);
 
 // ext.onExtensionUnloaded.addListener(deactivateBlockElement);
}