Firefox-based stealth example for avoid-blocking guide (interest check)

[feder-cr]

hey, before sending the PR i wanted to check if there'd be interest in adding an Invisible Firefox example to the avoid-blocking guide, mirroring the CloakBrowser example that landed in PR #1794 (merged 2026-03-31).

rationale: PR #1794 covers the Chromium-side path. some target sites flag Chromium UA by default and the same approach makes sense on the Firefox side. invisible_playwright (feder-cr/invisible_playwright) drives a patched Firefox 150 binary (feder-cr/invisible_firefox, MPL-2, same license as Firefox upstream, fingerprint patches at the C++ source code level so no JS shims to detect). it follows the same pip install + ensure_binary() + PlaywrightBrowserPlugin subclass pattern, so the integration shape is identical to the CloakBrowser one.

the draft PR #1921 mirrors the exact file structure of #1794: one new example file under docs/guides/code_examples/avoid_blocking/, one new section in docs/guides/avoid_blocking.mdx, plus the same versioned mirror under website/versioned_docs/version-1.7/. issues against the backend route to feder-cr/invisible_playwright.

if not in scope i'll close without noise.

[vdusek]

Mirrors my answer from #1921 here:

Hi @feder-cr, thanks for the PR, but we're going to pass on this one for now. We only want to showcase projects with an established track record and real-world adoption in our docs, and your project is still very new. However, we plan to add a new doc page on building custom extensions (#1936), which third-party integrations like yours could then link to. Closing.