Determine what manifest properties every vendor agrees on

[carlosjeurissen]

To move forward in describing webExtensions, seems it's productive to define the set of APIs and manifest keys which all vendors agree on.

We can then start building on that and proceed. My proposal is to start with a clean slate and only include the APIs and manifest keys which everyone agrees on. Otherwise we also have to include in our "spec" which APIs and what manifest keys are supported by what browsers / vendors in what situations which seems to be counter productive and as discussed before something which other places might be more suitable for like MDN.

[carlosjeurissen]

This has been discussed in the 2021-11-11 meeting.

To make sure we don't loose track of existing manifest keys. Here is an overview and where we can discuss them:
#113 - chrome_settings_overrides, chrome_url_overrides, incognito, omnibox
#108 - options_page
#67 - author, homepage_url, developer
#128 - sidebar_action
#50, #127 - action, browser_action, page_action
#283 - version, version_name

The following keys are not yet mentioned anywhere:
user_scripts, theme, storage