Subscribe links don't work on localhost

Environment

  • Ubuntu 20.04
  • Chrome 85
  • adblockpluschrome@next (last working version: Adblock Plus 3.9.5)

How to reproduce

  1. Create an HTML page with a subscribe link (e.g. <a href="https://subscribe.adblockplus.org/?location=https%3A//easylist-downloads.adblockplus.org/easylist.txt&title=EasyList">Subscribe</a>).
  2. Run local web server on port 8080.
  3. Navigate to http://localhost:8080/.
  4. Click on subscribe link.

Observed behavior

Extension's settings page opens asking user to confirm.

Expected behavior

Tab navigates to https://subscribe.adblockplus.org/.

Further information

This regression was introduced in #263 (closed) where we restricted subscribe links to only trusted domains. We then further restricted it to only HTTPS pages in #87 (closed).

Since we continued allowing filter lists that are served via non-HTTPS localhost, when we restricted them to only HTTPS in https://gitlab.com/eyeo/adblockplus/adblockpluscore/-/issues/5, we should also allow subscribe links on non-HTTPS localhost for testing purposes.