Change tabs with mousewheel in Firefox 57

ff57-tabs-mousewheel.js

// Change tabs with mousewheel
// Run into Browser Toolbox console

var onTabWheel = function(ev) {
  if (ev.deltaMode == 1 /* DOM_DELTA_LINE */) {
    var idx = gBrowser.tabContainer.getIndexOfItem(gBrowser.selectedTab);
    if (ev.deltaY > 0) {
      if (idx + 1 < gBrowser.tabs.length) {
        gBrowser.selectTabAtIndex(idx + 1);
      }
    } else if (ev.deltaY < 0) {
      if (idx > 0) {
        gBrowser.selectTabAtIndex(idx - 1);
      }
    }
  }
}

gBrowser.tabContainer.mTabstrip._scrollbox.addEventListener("wheel", onTabWheel);