This happens during the error page load. The error message:

Receiving unexpected Principal (http://localhost:4245/assets/www/hello.html) within RecvNewWindowGlobal

MOZ_Assert org.mozilla.geckoview.test  A  Assertion failure: false (Receiving unexpected Principal), at /Users/owlish/code/gecko/dom/ipc/ContentParent.cpp:1330

(http://localhost:4245/assets/www/hello.html is the error page address) Happens because we are trying to load an HTTP resource as the error page in the wrong process. HTTP as error pages is not something that we can easily support even if we implement a custom channel for async redirect to process switch (see bugs 1673763 and 1848701 for context).

What's needed here:

1. Make sure the undesirability of HTTP resource as the error page is communicated in the API documentation
2. Consider having URI validation in GeckoView
3. Change the error page URI in the tests

STR:

Run any of these with Fission enabled:

• NavigationDelegateTest#loadUnknownHost
• NavigationDelegateTest#loadUntrusted
• NavigationDelegateTest#safebrowsingPhishing
• NavigationDelegateTest#safebrowsingMalware
• NavigationDelegateTest#safebrowsingUnwanted
• NavigationDelegateTest#safebrowsingHarmful