HTTP Header Network Monitoring

HTTP Header Network Monitoring is a Firefox WebExtension for tracing HTTP traffic from the browser in a compact Network Monitor style UI.

Version 1.0.6 includes:

• Capture scope modes: locked tab, follow active tab, or all tabs.
• Locked tab mode also tracks child tabs opened from the locked tab when Firefox exposes the opener/source tab.
• Monitor window opens as a normal maximized window, so it can be resized/maximized like Firefox windows.
• Request selection for exporting only selected rows, with default export using the currently visible filtered list.
• Advanced blacklist rule window for hiding noisy requests by domain, URL, method, status, type, file, initiator, request header, or response header.
• Request table with sortable time, status, method, domain, file, type, transferred bytes, size, and duration columns.
• Resource filters include JSON in addition to HTML, CSS, JS, XHR, fonts, images, media, WebSocket, and other.
• Resizable detail pane with collapsible sections for headers, cookies, request body, response body, cache-related headers, and event timings.
• Icon copy buttons for URL, request text, response text, and individual detail sections.
• Request and response payloads default to raw view and can switch to beautified JSON/key-value views.
• Beautified URL-encoded/form payloads render as copyable key/value fields, JSON renders as an expandable tree, and HTML renders in a sandboxed preview.
• Request details can be opened in a separate window when the docked pane is too narrow.
• A DevTools panel is available so the monitor can be docked wherever Firefox Developer Tools are docked.
• Full response body capture while the monitor is open, with UI previews for text responses and binary payload export support.
• Edit and resend a selected request from the detail pane.
• Export captured traffic as HAR, JSON, JSONL, Markdown, or CSV.
• Optional sanitized export mode for sharing traces without header secrets or body text.

Unlike Firefox DevTools Network, this add-on is designed to keep session history across reloads, redirects, and page changes while the monitor window remains open. It is useful when you need to compare what changed from page to page instead of losing the trace on navigation.

The log is intentionally session-only: capture starts when the monitor UI opens and clears when the monitor is closed.