Programmatically uninstall an old version of an extension with a different UUID (i.e. loading new version with changed UUID would install side-by-side)

uninstall_extension.js

const {Cu} = require("chrome");
Cu.import("resource://gre/modules/AddonManager.jsm");

AddonManager.getAllAddons(function(aAddons) {
  // Here aAddons is an array of Addon objects
  var len = aAddons.length;
  console.log("Addons!");
  for (var i = 0; i < len; i++) {
    var addon = aAddons[i];
    console.log(addon.id, addon.name, addon.version, addon.isActive, addon.userDisabled);
    if (addon.name == "MyAddonName") {
      var version = addon.version.split(/\./);
      if (version[0] == "0" && (version[1] < "3" || (version[1] == "3" && version[2] < "4"))) {
        console.log("Old version! Uninstalling...", addon.version, version);
        addon.uninstall();
      }
    }
  }
});