Home screen opens to a page I can't change or remove.

As stated above, my Firefox opens to a page that I can't change or delete. I've tried new tab, new window, new private window close tab, close winder and still the original page remains underneath all the newly opened sites. In addition, I can't get into the page that keeps starting at the beginning, which needs a password but doesn't receive set new password email from the site manager. What can I do? I want to use Firefox and find this very frustrating.