Steps to reproduce

Tell us about your environment:

• Puppeteer version: 5.4.1
• Platform / OS version: Windows 10
• URLs (if applicable): N/A
• Node.js version: 12.13.0

What steps will reproduce the problem?

Please include code that reproduces the issue.

1. Use Puppeteer via a proxy
2. Provide proxy config via HTTP_PROXY / HTTPS_PROXY env vars and proxy / https-proxy NPM config
3. Set PUPPETEER_PRODUCT=firefox

What is the expected result?

Puppeteer's install.js should use the provided proxy config when downloading Firefox version metadata from https://product-details.mozilla.org/1.0/firefox_versions.json

What happens instead?

Download fails with ECONNREFUSED.

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The problem is that in install.ts, proxy options are configured for the binary data download but not for the Firefox metadata download.

This can be done via the https-proxy-agent package which is already a dependency (used in BrowserFetcher.ts). I'll look at submitting a PR.