It is impossible to register a chrome.manifest override for resource:// URIs.
It is possible to register a substitution for the migrator URI via ResProtocolHandler, but there is no chance we will load faster than nsBrowserGlue which will run the migration.
We could set browser.migration.version to 35 on install but meh.
resource://
URIs.browser.migration.version
to 35 on install but meh.