Press the <Alt Key> to bring up the tool bar. Then Tools > Options > General.

Option; When Firefox Starts should be set to Show My Home Page.

Option; Home Page. On the far right, press Restore To Default.
This will make your home page About:Home.

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If this does not work;
It could be the work of one of your add-ons, or even add / mal-ware. Look thru your add-ons list and make sure you know what each one is there for. Also, check the programs that are on your computer Windows > Start > Control Panel > Uninstall Programs. Go thru the list and use a web search to check any that you don't know what they are.

Troubleshoot Firefox Issues Caused By Malware

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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.

You can check if you have a user.js file in the Firefox profile folder that sets the browser.sessionstore.resume_session_once pref to true.

• http://kb.mozillazine.org/browser.sessionstore.resume_session_once

You can use this button to go to the currently used Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)

See also:

• http://kb.mozillazine.org/Preferences_not_saved