I don't use any of those preview/about:newtab/tab groups pages. But as far as i know, tab preview simply shows your open tabs. about:newtab shows tabs you visit the most. I doubt that's what you want. I think what you're looking for is Tab groups
, also known as Panorama from its earlier stage. But again, since i don't use any of this, i have no idea how this stuff works. At least you have the correct name now to search for and others can now correct me!
Since it has nothing to do with TMP, you can post your questions in that support.mozilla forum i linked.
there 2 other ways you can use to have those pages handy:
1. You can open all those tabs, Right click the tabbar > Bookmark all tabs and bookmark them in a special folder.
2. You can open all those tabs, set them as homepage (Fx Options/General > Use current pages) and then set Fx to start with your home page. Your browser will start with those tabs loaded. Of course, if you don't want them loaded, Tab groups seems to be your option.