Followup: as I'm migrating Indie Wiki Buddy to manifest 3 on Firefox,
it has required adding an additional permission
(declarativeNetRequest) to be able to inject the custom header into
BreezeWiki requests. Some users have expressed privacy concerns + it
has required Firefox users to approve the update, which is slowing
down users keeping the extension up to date.
As a result, I'm going to remove the custom header feature (at least
for the time being), and have Indie Wiki Buddy hide the IWB promo
banner + the indie wiki notice itself.