Maybe this help article help you,See:

• New Tab Page

Open a new window or tab. In the address bar, type about:Config. If a warning screen comes up, press the Be Careful button. This is where Firefox finds information it needs to run. At the top of the screen is a search bar. Enter browser.newtab.url and press enter. browser.newtab.url tells Firefox what to show when a new tab is opened. If you want, right click and select Modify. You can change the setting to;

about:home (Firefox default home page),
about:newtab (shows the sites most visited),
about:blank (a blank page),
or you can enter any web page you want.

The same instructions are used for the new window setting, listed as browser.startup.homepage.

If you use a "speed dial" extension for your home page, make sure it hasn't become disabled.

Open the Add-ons page. Either:

• Ctrl+Shift+a
• orange Firefox button (or Tools menu) > Add-ons

In the left column, click Extensions. Then check for the extension among the disabled extensions (lower list, gray background). Can you find it and enable it?

If it can't be enabled, you might need to update it. Use the "gear" button above the list > Check for Updates.

If it is enabled but is not showing on your home page, you may need to change your home page setting to whatever is compatible with the extension. For example, some have you set the home page to a blank page ("When Firefox starts: Show a blank page") in the options. This article shows where you set that: Startup, home page, tabs, and download settings.

If the above suggestions do not help, could you provide more information on what you're using for your home page? Thanks.

On rare occasions, Firefox may performed a "Reset" due to a problem upgrading. In that case, you will not have any of your extensions and there will be a new folder on your desktop named Old Firefox Data. If you find that folder, a volunteer could help you recover data from it.