Consider deferring browser download

[timvandermeij]

Currently the browsers for the tests are downloaded when npm install is invoked so that all test dependencies are present right away without further setup. This was also needed before because there was no way in Puppeteer to selectively download browsers at a later time.

However, nowadays Puppeteer exposes a separate browsers package/CLI. This could allow us to defer downloading of the actual browsers until the tests are actually started. This could be good for two reasons:

1. It avoids problem in e.g. the CI build if a new nightly release is published and the version rollover happens; see [Bug]: Get a 404 when trying to download Firefox during its version transition puppeteer/puppeteer#10414.
2. It will likely reduce the installation time which benefits the CI build too because it doesn't actually use the browsers.

[Sev6n]

Wow, this is a good proposal. Since it reduces installation times and improves CI efficiency. While Puppeteer is more associated with Chromium, it has Firefox support now.

You can install Firefox with @puppeteer/browsers:
Just use the npx @puppeteer/browsers install command, specifying Firefox.

npx @puppeteer/browsers install firefox@<version> --path ./browsers
(example): npx @puppeteer/browsers install firefox@114.0 --path ./browsers

Or if you want the stable version:
npx @puppeteer/browsers install firefox --path ./browsers

Now you can configure Puppeteer to use the Firefox you just installed. :)