From https://github.com/mongodb/js-bson/issues/330 :

Following the instruction in the section "Browser (no bundling)" doesn't work.

On line 3726, "global" is used, which is apparently not defined in browsers.

In Firefox:

ReferenceError: global is not defined                                  bson.bundle.js:3726:6
    BSON https://automower2/js/bson.bundle.js:3726
    <anonymous> https://automower2/js/bson.bundle.js:9112

Chrome has a similar error.

I'm not sure if this deserves a separate issue because it might be related. The "with bundling" section also has the same problem, and it seems the offending lines of code come from elsewhere:

if (typeof global.setTimeout === 'function') {
  cachedSetTimeout = setTimeout;
}

if (typeof global.clearTimeout === 'function') {
  cachedClearTimeout = clearTimeout;
}

one more...

var performance = global.performance || {};