You need to show a screenshot of that page for others to know what is going on. And where did you download Firefox browser from?

When you install Firefox, I think you get three pages: Welcome (with tips), Privacy Policy, and "Firefox Home" new tab page. You can close whichever tabs you don't find useful.

If the problem page isn't one of those, can you share its address? When you paste a URL here that doesn't go to a mozilla.org site, there could be a delay before your reply appears (this is an anti-spam feature of this site).