I. Notification Permission Telemetry

My first Firefox patch: adding Glean telemetry to track how users interact with notification permission prompts.

Bug 1998053 | D274203 | Reviewer: timhuang

The Problem

Firefox had limited visibility into how users interact with notification permission requests. We knew when permissions were granted or denied, but not:

• How often the permission icon appears vs. the full prompt
• Whether users click the icon or get the prompt automatically
• What percentage of requests are auto-blocked due to lack of user gesture
• How behavior differs across site categories (social media vs. productivity apps)

The Architecture

Firefox’s notification permission system has several layers:

1. DOM Layer (dom/notification/)

• Handles Notification.requestPermission() API calls
• Validates security context (HTTPS required)
• Checks for user gesture activation

2. Permission UI Layer (browser/modules/PermissionUI.sys.mjs)

• DesktopNotificationPermissionPrompt class
• Manages the permission dialog lifecycle
• Handles the “post-prompt” (shaking icon) flow
• This is where I added the new telemetry

3. Popup Notification System (browser/modules/PopupNotifications.jsm)

• Generic notification panel infrastructure
• Provides callbacks: onShown, onAfterShow, event callbacks

What I Built

Five Glean Event Metrics

web_notification_permission:
  icon_shown:
    description: Permission icon appears and animates in URL bar
  icon_clicked:
    description: User clicks the permission icon
  prompt_shown:
    description: Permission dialog displayed (script vs icon_click)
  prompt_blocked:
    description: Permission request auto-denied (no user gesture)
  prompt_interaction:
    description: User allows/blocks permission (with persistence)

Site Categorization System

Added a hardcoded map of 86 high-traffic domains across 8 categories:

const SITE_CATEGORIES = new Map([
  ["facebook.com", "social"],
  ["slack.com", "chat_communication"],
  ["mail.google.com", "email"],
  ["youtube.com", "media_streaming"],
  // ... 86 total domains
]);

function getSiteCategory(principal) {
  let host = principal.URI.host;
  if (SITE_CATEGORIES.has(host)) {
    return SITE_CATEGORIES.get(host);
  }
  // Check subdomain match
  for (let [domain, category] of SITE_CATEGORIES) {
    if (host.endsWith("." + domain)) {
      return category;
    }
  }
  return "other";
}

The Tricky Parts

Detecting Icon Click vs. Automatic Prompt

The challenge was distinguishing:

• Automatic: User clicked a button → site calls requestPermission() → prompt appears immediately
• Icon click: Site calls requestPermission() without gesture → icon appears → user clicks icon → prompt appears

Solution: check both the preference and the request’s hasValidTransientUserGestureActivation:

let trigger = "automatic";
if (
  this.requiresUserInput &&
  !this.request.hasValidTransientUserGestureActivation
) {
  trigger = "icon_click";
}

Finding the Right Callback Point

The telemetry had to go in the base PermissionPrompt class’s prompt() method, which wraps all actions—not in DesktopNotificationPermissionPrompt directly.

What I Learned

1. Firefox’s Permission System is Layered — DOM validates, UI presents, permission manager stores
2. Glean Telemetry is Code, Not Configuration — Metrics are defined in YAML but recorded in code
3. User Gestures Matter — hasValidTransientUserGestureActivation determines immediate vs. deferred prompts
4. The Permission Prompt is a State Machine — Not just “shown → allow/block” but a full lifecycle