Add more detail to storage.session docs (#24873)

- Remove "Chrome 122" from article, as the 10 MB limit is the quota that
  has been agreed upon across browsers.

- Clarify the duration that the storage is kept in memory.

- Clarify the access level of storage, mention the setAccessLevel API.
  The article does not exist yet, but can be written as part of
  https://bugzilla.mozilla.org/show_bug.cgi?id=1724754 and/or
  https://bugzilla.mozilla.org/show_bug.cgi?id=1687778

files/en-us/mozilla/add-ons/webextensions/api/storage/session/index.md

@@ -17,9 +17,10 @@ browser-compat: webextensions.api.storage.session
 
 {{AddonSidebar()}}
 
-Represents the `session` storage area. Items in `session` storage are stored in memory and are not persisted to disk.
+Represents the `session` storage area. Items in `session` storage are stored in memory for the duration of the browser session and are not persisted to disk.
+By default, it's not exposed to content scripts, but this behavior can be changed through {{WebExtAPIRef("storage.StorageArea.setAccessLevel", "storage.session.setAccessLevel()")}}.
 
-The browser may restrict the amount of data that an extension can store in the session storage area. For example, in Chrome 112, an extension is limited to storing 10MB of data in this storage area.
+The amount of data that an extension can store in the session storage area is limited to 10 MB, unless stated otherwise in the [browser compatibility table](#browser_compatibility).
 
 When the browser stops, all session storage is cleared. When the extension is uninstalled, its associated session storage is cleared.