Type about:preferences#general<enter> in the address bar.

There are two settings;

• When Firefox Starts

When the browser is started, what do you want to display? Many of us choose Show My Home Page.

• Home Page

When a new page is opened, what do you want to be displayed?

1. Use Current Page. Use what ever page(s) are open at that time.
2. Use Bookmark
3. Restore To Default. about:home shows a Mozilla home page with tools.

You can use any of these that you wish;

about:home (Firefox default home page), about:newtab (shows the sites most visited), about:blank (a blank page),

or you can enter any webpage or about: page you want.

Bookmark and use this; Download the Mozilla Search Reset {web link} This add-on is very simple: on installation, it backs up and then resets your search preferences and home page to their default values, and then uninstalls itself. This affects the search bar, URL bar searches, and the home page.

Hi   !
Your desktop shortcut might be corrupted. Here's how you can check that:

•   Desktop shortcut: right-click the icon, choose Properties
•   Pinned taskbar icon: right-click the icon, right-click Mozilla Firefox,     choose Properties
  

Windows normally will select the Shortcut tab. If not, go ahead and click the Shortcut tab.
The Target line should not have anything after this part:
32-bit Firefox on 64-bit Windows: "C:\Program Files (x86)\Mozilla Firefox\firefox.exe"
Otherwise: "C:\Program Files\Mozilla Firefox\firefox.exe"
If anything is listed after that, clear it out and save your change. To test, you can either:

•   Desktop shortcut: double-click the icon to launch a new window
•   Pinned taskbar icon: right-click the icon, click Mozilla Firefox to launch a new window
  

If you get a normal startup or a new window showing your home page, the shortcut is back to normal.