Figma use_figma Plugin API Rules
warpdotdev/warp
Required groundwork before any use_figma call: the rules and reference files for running JavaScript in a Figma file through the Plugin API without common failures.
Find and fix why a website is slow by capturing and analyzing a Firefox performance profile, or by analyzing a profile the user already has (a saved file or a profiler.firefox.com share link).
Install Web Performance
$ npx skills add mozilla/firefox-devtools-mcp --skill web-performance -a claude-codeProject install by default; add -g for ~/.claude/skills/.
$ gh skill install mozilla/firefox-devtools-mcp web-performance --agent claude-codeProject scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).
$ git clone --depth 1 https://github.com/mozilla/firefox-devtools-mcp.git skills-src && mkdir -p .claude/skills && cp -r skills-src/plugins/firefox-devtools-mcp/skills/web-performance .claude/skills/web-performance && rm -rf skills-srcUse ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.
Claude Code skills documentation · loads skills from .claude/skills/
Install the "web-performance" agent skill from https://github.com/mozilla/firefox-devtools-mcp/tree/main/plugins/firefox-devtools-mcp/skills/web-performance into .claude/skills/web-performance/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "web-performance", then confirm the skill loads.Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$skill-installer install https://github.com/mozilla/firefox-devtools-mcp/tree/main/plugins/firefox-devtools-mcp/skills/web-performanceType this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.
$ npx skills add mozilla/firefox-devtools-mcp --skill web-performance -a codexProject install goes to .agents/skills/; add -g for ~/.codex/skills/.
$ gh skill install mozilla/firefox-devtools-mcp web-performance --agent codexProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/mozilla/firefox-devtools-mcp.git skills-src && mkdir -p .agents/skills && cp -r skills-src/plugins/firefox-devtools-mcp/skills/web-performance .agents/skills/web-performance && rm -rf skills-srcUse ~/.agents/skills/ instead of .agents/skills for a personal install.
Codex skills documentation · loads skills from .agents/skills/
Install the "web-performance" agent skill from https://github.com/mozilla/firefox-devtools-mcp/tree/main/plugins/firefox-devtools-mcp/skills/web-performance into .agents/skills/web-performance/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "web-performance", then confirm the skill loads.Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add mozilla/firefox-devtools-mcp --skill web-performance -a cursorProject install goes to .agents/skills/; add -g for ~/.cursor/skills/.
$ gh skill install mozilla/firefox-devtools-mcp web-performance --agent cursorProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/mozilla/firefox-devtools-mcp.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/plugins/firefox-devtools-mcp/skills/web-performance .cursor/skills/web-performance && rm -rf skills-srcUse ~/.cursor/skills/ instead of .cursor/skills for a personal install.
Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/
Install the "web-performance" agent skill from https://github.com/mozilla/firefox-devtools-mcp/tree/main/plugins/firefox-devtools-mcp/skills/web-performance into .cursor/skills/web-performance/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "web-performance", then confirm the skill loads.Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gemini skills install https://github.com/mozilla/firefox-devtools-mcp.git --path plugins/firefox-devtools-mcp/skills/web-performance--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.
$ npx skills add mozilla/firefox-devtools-mcp --skill web-performance -a gemini-cliProject install goes to .agents/skills/; add -g for ~/.gemini/skills/.
$ gh skill install mozilla/firefox-devtools-mcp web-performance --agent gemini-cliProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/mozilla/firefox-devtools-mcp.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/plugins/firefox-devtools-mcp/skills/web-performance .gemini/skills/web-performance && rm -rf skills-srcUse ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.
Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/
Install the "web-performance" agent skill from https://github.com/mozilla/firefox-devtools-mcp/tree/main/plugins/firefox-devtools-mcp/skills/web-performance into .gemini/skills/web-performance/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "web-performance", then confirm the skill loads.Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gh skill install mozilla/firefox-devtools-mcp web-performanceInstalls for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).
$ npx skills add mozilla/firefox-devtools-mcp --skill web-performance -a github-copilotProject install goes to .agents/skills/; add -g for ~/.copilot/skills/.
$ git clone --depth 1 https://github.com/mozilla/firefox-devtools-mcp.git skills-src && mkdir -p .github/skills && cp -r skills-src/plugins/firefox-devtools-mcp/skills/web-performance .github/skills/web-performance && rm -rf skills-srcUse ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.
GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/
Install the "web-performance" agent skill from https://github.com/mozilla/firefox-devtools-mcp/tree/main/plugins/firefox-devtools-mcp/skills/web-performance into .github/skills/web-performance/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "web-performance", then confirm the skill loads.GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add mozilla/firefox-devtools-mcp --skill web-performance -a opencodeOpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.
$ gh skill install mozilla/firefox-devtools-mcp web-performance --agent opencodeProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/mozilla/firefox-devtools-mcp.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/plugins/firefox-devtools-mcp/skills/web-performance .opencode/skills/web-performance && rm -rf skills-srcUse ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.
OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/
Install the "web-performance" agent skill from https://github.com/mozilla/firefox-devtools-mcp/tree/main/plugins/firefox-devtools-mcp/skills/web-performance into .opencode/skills/web-performance/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "web-performance", then confirm the skill loads.OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
Facts
- Skill name
web-performance- GitHub stars
- 468
- Token cost
- ~1.2k tokens
- SKILL.md length
- 652 words
- Files
- 4 (incl. references)
- Skills in repo
- 6
- Repo updated
- First seen
- Licence
- Custom licence
At a glance
Find and fix why a website is slow by capturing and analyzing a Firefox performance profile, or by analyzing a profile the user already has (a saved file or a profiler.firefox.com share link).
- Works in 8 steps: Prerequisites → Pick the scenario → Capture → …
- Slow page loads
- SKILL.md covers Step 0: Prerequisites, Step 1: Pick the scenario, Step 2: Capture and Step 3: Analyze, plus 4 more sections
- Calls npm and npx
What it does
Web Performance is an agent skill from mozilla/firefox-devtools-mcp. Find and fix why a website is slow by capturing and analyzing a Firefox performance profile, or by analyzing a profile the user already has (a saved file or a profiler.firefox.com share link). Use for slow page loads, janky scrolling or animation, slow interactions or a slow STR, long tasks, layout thrashing, or heavy JavaScript.
Its SKILL.md is about 1.2k tokens, which your agent loads only when the skill is triggered. The skill folder holds 4 other files, including reference files (for example `references/analysis-playbook.md`, `references/capture-recipes.md` and `references/validation.md`).
It sits in Frontend & Design, covering Web performance and Performance optimization. It works with JavaScript and Model Context Protocol. The repository describes itself as: Model Context Protocol server for Firefox DevTools - enables AI assistants to inspect and control Firefox browser through WebDriver BiDi.
When your agent uses it
- Slow page loads
- Janky scrolling
- Slow interactions
- Layout thrashing
Example prompts
- “/web-performance”
Requirements
- Node.js
Workflow steps
8 steps, taken from the step headings in SKILL.md.
- Prerequisites
- Pick the scenario
- Capture
- Analyze
- Find the cause in the source
- Report with explicit confidence
- Fix and verify
- Clean up
What it can do on your machine
Read from SKILL.md and the folder at commit 5c69888. It shows what the files ask for, not the result of running them.
Tool permissions
Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.
From allowed-tools in the SKILL.md frontmatter.
Runs code
Shell commands in SKILL.md call:
npmnpx
From the folder's file list and the shell code blocks in SKILL.md.
Network
No URLs in SKILL.md. Its commands use npm and npx, which can reach the network depending on how they are called.
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names no API keys, tokens, secrets or passwords.
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.
Context cost
Web Performance loads about 1.2k tokens when it runs, and up to ~4.3k if it reads all its reference files. Until then it costs about 87 tokens; SKILL.md has 652 words of instructions outside code blocks.
Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.
Safety
Auto-check passed
The automated check found no risky patterns in SKILL.md.
Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.
SKILL.md
Its licence (Custom licence) doesn't allow us to republish the file, so here is its outline and opening line. It has 652 words (~1,188 tokens).
“Work from a real profile, find the cause in the user's code, report it honestly, and if asked, fix it and prove the fix worked. The firefox-devtools MCP drives Firefox and records a profile when there is none yet; profiler-cli…”
- name
- web-performance
Files
SKILL.md and 3 other files (references) in plugins/firefox-devtools-mcp/skills/web-performance of mozilla/firefox-devtools-mcp.
- SKILL.md
- references/analysis-playbook.md
- references/capture-recipes.md
- references/validation.md
Open the folder on GitHubat commit 5c69888
Compare with similar skills
Web Performance next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.
| Skill | Stars | Used in | Tokens | Auto-check | Licence | Repo updated |
|---|---|---|---|---|---|---|
| Web Performance this skillmozilla/firefox-devtools-mcp | 468 | — | ~1.2k | Automated safety check: Pass | Custom licence | |
| Figma use_figma Plugin API Ruleswarpdotdev/warp | 65k | 4 repos | ~4.4k | Automated safety check: Pass | AGPL-3.0 | |
| Performancemidudev/100cosas.dev | 114 | 6 repos | ~2.3k | Automated safety check: Pass | MIT | |
| I Optimizeboussadjra/vuestrata | 111 | 11 repos | ~1.9k | Automated safety check: Pass | MIT | |
| Compare Array Bundle SizePostHog/posthog-js | 613 | — | ~599 | Automated safety check: Pass | Custom licence | |
| Servo Fetchkonippi/servo-fetch | 156 | — | ~1.9k | Automated safety check: Pass | Apache-2.0 |
Similar skills
Performance
midudev/100cosas.dev
Optimize web performance for faster loading and better user experience.
I Optimize
boussadjra/vuestrata
Improve interface performance across loading speed, rendering, animations, images, and bundle size.
- Official
Compare Array Bundle Size
PostHog/posthog-js
Quickly compare the posthog-js array.js bundle size in the current working tree against a git baseline using the repository's esbuild proxy.
Servo Fetch
konippi/servo-fetch
Fetch and render web pages using the Servo browser engine — a single binary with JS execution, CSS layout, screenshots, and content extraction.
Web Perf
hodgef/apiker
Analyzes web performance using Chrome DevTools MCP. An agent skill from hodgef/apiker.
More from mozilla/firefox-devtools-mcp
Browser Automation
mozilla/firefox-devtools-mcp
This skill should be used when the user asks about browser automation, testing web pages, extracting content, filling forms, taking screenshots, or monitoring console/network activity.
Firefox Devtools Diagnose
mozilla/firefox-devtools-mcp
Diagnose Firefox DevTools MCP setup issues. An agent skill from mozilla/firefox-devtools-mcp.
Debug
mozilla/firefox-devtools-mcp
Show console errors and failed network requests. An agent skill from mozilla/firefox-devtools-mcp.
Navigate
mozilla/firefox-devtools-mcp
Navigate Firefox to a URL and take a DOM snapshot for interaction
Screenshot
mozilla/firefox-devtools-mcp
Take a screenshot of a URL or the current page. An agent skill from mozilla/firefox-devtools-mcp.
Related
Works with
Categories
Questions about Web Performance
What does Web Performance do?
Find and fix why a website is slow by capturing and analyzing a Firefox performance profile, or by analyzing a profile the user already has (a saved file or a profiler.firefox.com share link). Web Performance is an agent skill from mozilla/firefox-devtools-mcp.com share link).
When should I use Web Performance?
Web Performance fits situations like: slow page loads; janky scrolling; slow interactions; layout thrashing.
How do I install Web Performance in Claude Code?
Run `npx skills add mozilla/firefox-devtools-mcp --skill web-performance -a claude-code`. Or copy the skill folder (plugins/firefox-devtools-mcp/skills/web-performance in mozilla/firefox-devtools-mcp) into .claude/skills/web-performance in your project. Claude Code loads it when a task matches its description.
How do I install Web Performance in Codex?
Run `npx skills add mozilla/firefox-devtools-mcp --skill web-performance -a codex`. Or copy the skill folder (plugins/firefox-devtools-mcp/skills/web-performance in mozilla/firefox-devtools-mcp) into .agents/skills/web-performance in your project. Codex loads it when a task matches its description.
Can I use Web Performance in Cursor, Gemini CLI or GitHub Copilot?
Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add mozilla/firefox-devtools-mcp --skill web-performance -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/web-performance, .gemini/skills/web-performance, .github/skills/web-performance and .opencode/skills/web-performance in your project.
What does Web Performance need to run?
Going by SKILL.md and its folder, Web Performance needs the command-line tools its instructions call (npm and npx). Our summary lists: Node.js.
Does Web Performance access the network?
SKILL.md contains no URLs. Its commands use npm and npx, which can reach the network depending on how they are called. This is read from the text; nothing was executed.
Is Web Performance safe to install?
Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.
What licence does Web Performance use?
Web Performance has a licence file (the repository's licence) that doesn't match a standard licence. Read it on GitHub before reusing the skill.
How many tokens does Web Performance use?
About 1.2k tokens (SKILL.md is roughly 4.8k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full. Its references folder adds about 3.1k tokens, read only when the agent opens those files.
What are the alternatives to Web Performance?
Skills that share tags, products or a category with Web Performance: Figma use_figma Plugin API Rules (warpdotdev/warp, 65k stars), Performance (midudev/100cosas.dev, 114 stars), I Optimize (boussadjra/vuestrata, 111 stars) and Compare Array Bundle Size (PostHog/posthog-js, 613 stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.
Who maintains Web Performance?
mozilla (a GitHub organization) maintains it in mozilla/firefox-devtools-mcp, which has 468 GitHub stars. The repository holds 6 skills in this directory. The repository was last updated on October 6, 2026.
Source: mozilla/firefox-devtools-mcp on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.