Custom homepage/new tab stays open when opening container tabs

[Rob--W]

Moved from https://bugzilla.mozilla.org/show_bug.cgi?id=1715770

Steps to reproduce

1. Set https://amazon.com to always open in a container tab

Scenario 1:

1. Change homepage to https://google.com
2. Open a new window, or click the "home" button
3. Open https://amazon.com

Scenario 2:

1. Install nightTab extension (or something similar that replaces the default new tab page) and enable it as the new tab page
2. Open a new tab
3. Open https://amazon.com

Actual behavior

Amazon opened in a new container tab, separate from the home/new tab page we were on previously. We now have two tabs open.

Expected behavior

The home/new tab page should have been replaced by the container tab, as it would happen if you are using the default. There should be only one tab open.

Notes

This issue was moved from https://bugzilla.mozilla.org/show_bug.cgi?id=1715770