Clarify auto-generation of background service worker

[dotproto]

Summary

This PR addresses the following feedback raised in another PR.

@rebloor can we add a note stating Firefox does not support generating a service_worker based in the scripts key? This is something currently only supported by Apple.

Originally posted by @carlosjeurissen in #25808 (comment)

Test results and supporting details

N/A

Related issues

• Firefox 136 supports webextensions.manifest.background.preferred_environment #25808
• Bugzilla 1930334: Implement background.preferred_environment

[rebloor]

@dotproto but Firefox doesn't support service workers anyway, so why would there be an expectation that it would generate a background service worker? I think this note could be potentially confusing. Also, we provide more comprehensive information on the manifest key page: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/background#browser_support

[github-actions]

This pull request has merge conflicts that must be resolved before it can be merged.

[carlosjeurissen]

The current wording implies firefox would auto-generate a background service worker if scripts and preferred_environment are not specified in background. However Firefox simply never auto-generates a serviceWorker and only loads a serviceWorker if set explicitly in background.service_worker and serviceWorkers are enabled in the browser.

[carlosjeurissen]

@rebloor Safari does auto generate a service worker. However this is not common knowledge and the current wording in this PR indeed causes more confusion than it removes.

[rebloor]

@dotproto have you had a chance to review the feedback?

[rebloor]

Supercedeed by mdn/content#40825