web-performancelisted

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` queries the profile, whether you captured it or the user brought it. Report in web-platform terms (LCP, main-thread blocking, reflow, render-blocking resources), not Gecko internals - unless the target is Firefox itself rather than a page, in which case platform frames are the subject and the fix lands in mozilla-central. ## Step 0: Prerequisites profiler-cli needs Node.js >= 24: ```bash command -v profiler-cli >/dev/null 2>&1 || npm install -g @firefox-devtools/profiler-cli@latest ``` `npx @firefox-devtools/profiler-cli@latest` also works but re-resolves on every call. The rest of this step is only for capturing. Skip it when the user already has a profile. The profiler tools need **Firefox 154+**. Check with `get_firefox_info`, which also launches it. If Firefox is missing or older, stop and ask the user to install a current release or point the server at one with `--firefox-path`. The profiler tools also need the `developer` tool preset: if `profiler_start` is absent, ask the user to restart the server with `--tool-preset developer`, since the default `basic` preset has no profiler. ## Step 1: Pick the scenario **If the user already has a profile** - a saved `.json.gz`, or a `share.firefox.dev` / profiler.firefox.com link - there is nothing t