Clarify sharing objects with page scripts impact on build a cross browser extension

[rebloor]

MDN URL

https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Build_a_cross_browser_extension

What specific section or headline is this issue about?

No response

What information was incorrect, unhelpful, or incomplete?

Firefox supports a mechanism to use window.promise to create a Promise accessible to the webpage from content scrip. This mechanism is explained on the Sharing objects with page scripts page but not clarified on Build_a_cross_browser_extension.

What did you expect to see?

Information on Build_a_cross_browser_extension about passing a promise, linking to (https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Sharing_objects_with_page_scripts)

Do you have any supporting links, references, or citations?

No response

Do you have anything more you want to share?

No response

[Rob--W]

This can be resolved by adding a section to https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Build_a_cross_browser_extension that highlights the differences between content script execution contexts:
https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/Content_scripts#content_script_environment

Although not part of this issue originally, it's also worth removing the "December 2021" banner at the top, and to make the content up-to date:

• API asynchronous event handling section: Chrome's MV3 supports promises.
• A section that mentions the existence of Manifest V2 and Manifest V3. The current content at https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/manifest.json/manifest_version is unfortunately very sparse... I think that I may have to bootstrap additional content for that article. For now the bare minimum could be to link to the MV2->MV3 migration guides from Firefox and Chrome: https://extensionworkshop.com/documentation/develop/manifest-v3-migration-guide/ and https://developer.chrome.com/docs/extensions/migrating/
• Link the background "Browser support" section that was added in Background page load fail bug fix release note #30097