Change tabs with mousewheel in Firefox 57

ff57-tabs-mousewheel.js

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

function onTabWheel(ev) {
  if (ev.deltaMode == 1 /* DOM_DELTA_LINE */) {
    var idx = Array.prototype.slice.call(gBrowser.tabs).indexOf(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.tabs.forEach(function(tab) {
  tab.addEventListener("wheel", onTabWheel);
});

var tabObserver = new MutationObserver(function(records, observer) {
  records.forEach(function(record) {
    record.addedNodes.forEach(function(tab) {
      tab.addEventListener("wheel", onTabWheel);
    });
    record.removedNodes.forEach(function(tab) {
      tab.removeEventListener("wheel", onTabWheel);
    });
  });    
});
tabObserver.observe(gBrowser.tabContainer, {childList: true});

Hey, I tried running your code but I get an error saying "gBrowser is not defined".
Any ideas?

Did your try to run it in the Browser Toolbox?

I get the same error in Fx59. :( I put it in Browser Toolbox console.

TypeError: gBrowser.tabContainer.mTabstrip is undefined

works for me, thanks! is there a way to run this on startup?

@Keith94 The first revision of the gist doesn't use mTabstrip. It might work with your version.

@fm3 Not that I know of. :(

The lastest version doesn't works with Firefox 58, but the first version works well.

Vote here to integrate this feature natively.

For compatibility with Firefox 58, in my fork I changed mTabstrip._scrollbox to arrowScrollbox. They renamed it in 1415537