[ffpip]

Try

Type about:config in URL bar -> click proceed -> Search "browser.startup.homepage_override.mstone" in the shown search bar -> change value to "ignore"

https://kb.mozillazine.org/Startup.homepage_override_url

[qwertox]

Thanks, this looks promising.

I hope it also works with the "last session" tabs and doesn't pop up a homepage (If browser.startup.homepage_override.mstone is set to “ignore”, the browser’s homepage will not be overridden after updates.).

I love Firefox's about:config page, it has so many options.