browser.startup.homepage and TOR_DEFAULT_HOMEPAGE are ignored for the new window opened by New Identity

Summary

In 13.0, the browser.startup.homepage pref (and hence also the TOR_DEFAULT_HOMEPAGE environment variable, which populates the pref) is no longer used for the initial new window that is opened by New Identity. This new window uses about:tor instead.

Steps to reproduce:

1. Run TOR_DEFAULT_HOMEPAGE='https://example.com/' ./start-tor-browser
2. Connect
3. Trigger New Identity

Environment

Linux (x86_64)