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Agent skill

Perf Regression Triage

by mozilla-firefox in mozilla-firefox/firefox

Handle a Perfherder performance regression bug end to end: read the alert bug, confirm whether the regression is real, find the cause, and iterate to a fix.

Custom licenceAuto-check passedTesting & QA

Install Perf Regression Triage

skills CLI
$ npx skills add mozilla-firefox/firefox --skill perf-regression-triage -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install mozilla-firefox/firefox perf-regression-triage --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/mozilla-firefox/firefox.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.agents/skills/perf-regression-triage .claude/skills/perf-regression-triage && rm -rf skills-src

Use ~/.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/

Facts

Skill name
perf-regression-triage
GitHub stars
13k
Token cost
~1.7k tokens
SKILL.md length
837 words
Files
6 (incl. references)
Skills in repo
7
Repo updated
First seen
Licence
Custom licence

At a glance

Handle a Perfherder performance regression bug end to end: read the alert bug, confirm whether the regression is real, find the cause, and iterate to a fix.

  • Works in 5 steps: read the bug → confirm it → find the cause → …
  • The user has a Perfherder/browsertime regression bug (the N% <test ..
  • SKILL.md covers Tooling, Step 1: read the bug, Step 2: confirm it and Step 3: find the cause, plus 3 more sections
  • Runs Shell scripts from its folder; calls npm and git

What it does

Perf Regression Triage is an agent skill from mozilla-firefox/firefox. Handle a Perfherder performance regression bug end to end: read the alert bug, confirm whether the regression is real, find the cause, and iterate to a fix. Use when the user has a Perfherder/browsertime regression bug (the "N% <test ... regression on <date" bugs filed in Testing::Performance), needs to establish whether an alert summary is a real regression, is interpreting a PerfCompare baseRev/newRev comparison, or asks what to do about a patch of theirs that regressed a benchmark. Not for simply running perf…

Its SKILL.md is about 1.7k tokens, which your agent loads only when the skill is triggered. The skill folder holds 7 other files, including reference files (for example `references/close-out.md`, `references/confirm.md` and `references/iterate.md`).

It sits in Testing & QA, covering Performance optimization and Failing and flaky tests. The repository describes itself as: The official repository of Mozilla's Firefox web browser.

When your agent uses it

  • The user has a Perfherder/browsertime regression bug (the N% <test ..
  • Tasks that involve Performance optimization
  • Tasks that involve Failing and flaky tests

Example prompts

  • “N% <test ... regression on <date”
  • “/perf-regression-triage”

Requirements

  • Node.js
  • A Bash shell
  • Pre-approved tools (allowed-tools): Bash(./mach try perf --help:*), Bash(./mach try perf --no-push:*), Bash(treeherder-cli:*), Bash(profiler-cli:*), Bash(curl -s 'https://treeherder.mozilla.org/api/:*), Bash(git log:*), Bash(git show:*), Bash(git status:*), Bash(jj log:*), Bash(hg log:*), mcp__moz__get_bugzilla_bug, Read, Grep, Glob

Workflow steps

5 steps, taken from the step headings in SKILL.md.

  1. read the bug
  2. confirm it
  3. find the cause
  4. iterate to a fix
  5. close out

What it can do on your machine

Read from SKILL.md and the folder at commit 8477c6d. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves these tools, so the agent can use them without asking each time:

    • Bash(./mach try perf --help:*)
    • Bash(./mach try perf --no-push:*)
    • Bash(treeherder-cli:*)
    • Bash(profiler-cli:*)
    • Bash(curl -s 'https://treeherder.mozilla.org/api/:*)
    • Bash(git log:*)
    • Bash(git show:*)
    • Bash(git status:*)
    • Bash(jj log:*)
    • Bash(hg log:*)

    …and 4 more on the same allowed-tools line.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    Ships script files (Shell), which the agent can run.

    Shell commands in SKILL.md call:

    • npm
    • git

    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 git, 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

Perf Regression Triage loads about 1.7k tokens when it runs, and up to ~7.1k if it reads all its reference files. Until then it costs about 232 tokens; SKILL.md has 837 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~232
When it runs · the whole SKILL.md, loaded when a task matches
~1.7k
With references · SKILL.md plus every file in references/, read only if the agent opens them
~7.1k

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 837 words (~1,747 tokens).

“Three tools cover the three kinds of evidence in a regression bug. Use them rather than fetching URLs by hand — WebFetch on a Treeherder or profiler URL returns a UI shell with no data in it.”

— opening of SKILL.md by mozilla-firefox, Custom licence
name
perf-regression-triage
allowed-tools
Bash(./mach try perf --help:*), Bash(./mach try perf --no-push:*), Bash(treeherder-cli:*), Bash(profiler-cli:*), Bash(curl -s 'https://treeherder.mozilla.org/api/:*), Bash(git log:*), Bash(git show:*), Bash(git status:*), Bash(jj log:*), Bash(hg log:*), mcp__moz__get_bugzilla_bug, Read, Grep, Glob

Read the full SKILL.md on GitHub

Files

SKILL.md and 5 other files (references) in .agents/skills/perf-regression-triage of mozilla-firefox/firefox.

  • SKILL.md
  • references/close-out.md
  • references/confirm.md
  • references/iterate.md
  • references/rest-api.md
  • tests/trigger-tests.sh

Open the folder on GitHubat commit 8477c6d

Compare with similar skills

Perf Regression Triage 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.

Perf Regression Triage compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
Perf Regression Triage this skillmozilla-firefox/firefox13k—~1.7kAutomated safety check: PassCustom licence
Code SolvingHoangTheQuyen/think-better122—~3.7kAutomated safety check: PassMIT
Pester Failure AnalysisPowerShell/PowerShell56k—~5.1kAutomated safety check: PassMIT
Browser Testing with Chrome DevToolsaddyosmani/agent-skills103k4 repos~3.5kAutomated safety check: WarnMIT
Apple Container Test RunnerRustPython/RustPython22k—~467Automated safety check: PassMIT
Testingkortix-ai/suna20k—~3.6kAutomated safety check: NotesCustom licence

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Categories

Questions about Perf Regression Triage

What does Perf Regression Triage do?

Handle a Perfherder performance regression bug end to end: read the alert bug, confirm whether the regression is real, find the cause, and iterate to a fix. Perf Regression Triage is an agent skill from mozilla-firefox/firefox. Handle a Perfherder performance regression bug end to end: read the alert bug, confirm whether the regression is real, find the cause, and iterate to a fix.

When should I use Perf Regression Triage?

Perf Regression Triage fits situations like: the user has a Perfherder/browsertime regression bug (the N% <test .; tasks that involve Performance optimization; tasks that involve Failing and flaky tests.

How do I install Perf Regression Triage in Claude Code?

Run `npx skills add mozilla-firefox/firefox --skill perf-regression-triage -a claude-code`. Or copy the skill folder (.agents/skills/perf-regression-triage in mozilla-firefox/firefox) into .claude/skills/perf-regression-triage in your project. Claude Code loads it when a task matches its description.

How do I install Perf Regression Triage in Codex?

Run `npx skills add mozilla-firefox/firefox --skill perf-regression-triage -a codex`. Or copy the skill folder (.agents/skills/perf-regression-triage in mozilla-firefox/firefox) into .agents/skills/perf-regression-triage in your project. Codex loads it when a task matches its description.

Can I use Perf Regression Triage 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/firefox --skill perf-regression-triage -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/perf-regression-triage, .gemini/skills/perf-regression-triage, .github/skills/perf-regression-triage and .opencode/skills/perf-regression-triage in your project.

What does Perf Regression Triage need to run?

Going by SKILL.md and its folder, Perf Regression Triage needs a shell for the scripts in its folder and the command-line tools its instructions call (npm and git). Our summary lists: Node.js; A Bash shell. Its frontmatter pre-approves these tools: Bash(./mach try perf --help:*), Bash(./mach try perf --no-push:*), Bash(treeherder-cli:*), Bash(profiler-cli:*), Bash(curl -s 'https://treeherder.mozilla.org/api/:*), Bash(git log:*), Bash(git show:*), Bash(git status:*), Bash(jj log:*), Bash(hg log:*), mcp__moz__get_bugzilla_bug, Read, Grep, Glob.

Does Perf Regression Triage access the network?

SKILL.md contains no URLs. Its commands use npm and git, which can reach the network depending on how they are called. This is read from the text; nothing was executed.

Is Perf Regression Triage 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 Perf Regression Triage use?

Perf Regression Triage 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 Perf Regression Triage use?

About 1.7k tokens (SKILL.md is roughly 7k 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 5.3k tokens, read only when the agent opens those files.

What are the alternatives to Perf Regression Triage?

Skills that share tags, products or a category with Perf Regression Triage: Code Solving (HoangTheQuyen/think-better, 122 stars), Pester Failure Analysis (PowerShell/PowerShell, 56k stars), Browser Testing with Chrome DevTools (addyosmani/agent-skills, 103k stars) and Apple Container Test Runner (RustPython/RustPython, 22k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Perf Regression Triage?

mozilla-firefox (a GitHub organization) maintains it in mozilla-firefox/firefox, which has 13,402 GitHub stars. The repository holds 7 skills in this directory. The repository was last updated on October 9, 2026.

Source: mozilla-firefox/firefox on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.