Browser notifications not working in Firefox Add-on

Question

I am using Windows 7 and developing a Firefox add-on that needs to display notifications, but none are being displayed. I have confirmed that the command browser.notifications.create is being executed in the background script and the returned promise fulfilled with an ID.

I ran a regression on Firefox builds using Mozilla's mozregression tool along with their notifications example at https://github.com/mdn/webextensions-examples/tree/master/notify-link-clicks-i18n. I found that the last known good build was on 2018-09-25, and the next day's build was bad. The tool gave me a response of "Unable to find enough data to bisect"

I searched Bugzilla but found nothing, which seemed strange since apparently this issue is over 2 years old. So before I submit a bug report, does anyone have any ideas what the issue might be?

Edit: As requested, here's the code

browser.notifications.create({
    "type": "basic",
    "iconUrl": browser.extension.getURL("icons/link-48.png"),
    "title": title,
    "message": content
});