It takes you back to page 12 when you backspace/ back arrow because that was the last page you viewed prior to clicking page 1. If you want to go back to the home page, click on "home" at the top where it says home, forums, gallery. You can also click on forums to view all the forums which will take you to a listing of threads inside each one when you click on them. Also check your browser cookies, because this forum requires you to allow them to navigate successfully when signed in. You can still view/ post without them, but it can get annoying with all the little extra steps. Hope that helps.
Going back to main thread you are viewing: there should be a chain of links right above the thread's name and below the ads.