How to create a one-time onBeforeSendHeaders listener?

Question

I'm using the webRequest.onBeforeSendHeaders API to modify the headers of some HTTP requests. My problem is that each event listener should only be executed once, but for some reason the event listener can't modify the HTTP request and disconnect itself.

Here's a little demo:

function addReferrer(e){
    // This line prevents the function from doing its job
    browser.webRequest.onBeforeSendHeaders.removeListener(addReferrer)

    e.requestHeaders.push({
        name: 'Referer',
        value: 'https://fake.referrer'
    })
    return {requestHeaders: e.requestHeaders}
}

browser.webRequest.onBeforeSendHeaders.addListener(
    addReferrer,
    {urls: ['https://shouldiblamecaching.com/']},
    ["blocking", "requestHeaders"]
)

This is supposed to add a Referer header when you visit https://shouldiblamecaching.com/, but because of the removeListener(addReferrer), it doesn't. (You can test this with the "Network" tab in the browser console.) (Tested with Firefox, not sure if it works in other browsers.)

Workarounds I've tried:

1. Disconnect with setTimeout(..., 1)
2. Adding a 2nd listener that disconnects both listeners

Is there a clean way to create a one-shot event listener?