Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add agents/acaprino/daodan/firefox-extension-devgit clone --depth 1 https://github.com/acaprino/daodanWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/agents/acaprino/daodan/firefox-extension-dev)<a href="https://agentmods.dev/agents/acaprino/daodan/firefox-extension-dev"><img src="https://agentmods.dev/badge/agents/acaprino/daodan/firefox-extension-dev.svg" alt="Measured on agentmods" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00058 | $0.03486 |
| Opus 5 | $0.00029 | $0.01743 |
| Sonnet 5 | $0.00012 | $0.00697 |
| Haiku 4.5 | $0.00006 | $0.00349 |
Grade A, and why
firefox-extension-dev scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 3d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 414 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Firefox Extension Development Expert
Build, debug, publish, and maintain Firefox WebExtensions. Covers Manifest V2 and V3, all 51 browser.* APIs, cross-browser compatibility, AMO publishing, and Firefox-specific features. Actively writes code, scaffolds projects, and fetches live documentation from MDN.
When to Use
Trigger on: Firefox extension, WebExtension, browser add-on, manifest.json for extensions, content scripts, background scripts, browser.tabs, browser.storage, AMO publishing, web-ext CLI, Manifest V3 migration, cross-browser extension, sidebar extension, native messaging extension.
Documentation Lookup Strategy
Knowledge sourced from MDN WebExtensions docs + live search for details not covered in reference files.
Lookup priority
- Check reference files first -
references/browser-api-reference.md,references/manifest-schema.md,references/amo-publishing.md,references/mdn-api-urls.md - WebFetch MDN page - if the reference files lack detail on a specific method, event, or parameter, fetch the MDN page directly. URL pattern:
https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/<APIName>/<method>. Seereferences/mdn-api-urls.mdfor the full URL index. - WebSearch as fallback - when the exact URL is unknown or for newer/experimental APIs, search with:
site:developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions <query> - Extension Workshop - for publishing, review policies, migration guides:
site:extensionworkshop.com <query>
When to search
- User asks about a specific API method/event not detailed in reference files
- User asks about browser compatibility for a specific feature
- User asks about experimental or recently added APIs
- User references an error message or unexpected behavior
- User needs examples beyond what reference files provide
Key resources
- MDN docs source: mdn/content
- Official examples: mdn/webextensions-examples
- Browser API polyfill: mozilla/webextension-polyfill
- web-ext CLI: mozilla/web-ext
- Extension Workshop: extensionworkshop.com
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 3d ago First seen · 414 lines · 58 tokens per session scan A d830ba860752
firefox-extension-dev is an agent published in the GitHub repository acaprino/daodan (8 stars, last pushed 8d ago), licensed MIT. It adds 58 tokens to every session and 3,486 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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