Resolve an inconsistency between Chrome and Firefox with how the
contentscript runs in an iframe.
This should have no user-facing impact, it's just meant as a safeguard
in case something unintentionally gets included in the contentscript.
The web accessible resources were removed in #14834, but they were
accidentally preserved in the v3 manifest. We no longer need any web
accessible resources, and leaving these in the manifest exposes us to
potential security issues.
This reverts commit f09ab88891, reversing
changes made to effc761e0e.
This is being temporarily reverted to make it easier to release an
urgent fix for v10.15.1.
Ariella Vu
Mark Stacey
David Walsh
Dan Miller
Jyoti Puri