"New Tab" that is.

When you load your home page, it definitely should display the title from the page. If you reload the page (Ctrl+r or click the Home icon again) does Firefox catch on to that?

On the other hand, if you use an add-on to substitute that same page for Firefox's usual new tab page (the one displayed when you click the + button or press Ctrl+t), it might not behave normally there; the coding for that page is rather unusual.

Does that distinction seem relevant here?

When I reload the page, it shows the correct title of the page.

It's only when I open the browser for the first time, or restart Firefox, that it shows New Tab instead of the title.

I disabled my add-ons but couldn't get it to do it again.

It doesn't do it every time, but I did notice it today after updating Firefox to the latest version. I wonder if that's the mode when it happens and that's why it's intermittent.

I'll monitor it next time it happens and see what other clues I can find.