Related issue:
https://github.com/uBlockOrigin/uBOL-home/issues/325
This is a first version, with support only for custom filters which are
plain CSS selectors. Future versions will extend support to style-based
and procedural cosmetic filters.
Manually text-editing existing custom filters is currently not supported,
this will be added in a future version in the Develop pane. To remove
existing custom filters, the "Remove a custom filter" tool can be used.
Call to postMessage was failing in the zapper when using `use_dynamic_url` in
manifest. Manually overwriting the per-session dynamic hostname with the real
extension id fixes this.
