Hi,
It sounds like a setting was changed on your new tab page. These changes are usually caused by third-party toolbars or add-ons. I understand that you would like to know how to change it back. Not a problem, please follow the steps below:
- In the Location bar, type about:config and press Enter. The "This might void your warranty!" warning page may appear.
- Click I'll be careful, I promise! to continue to the about:config page.
- Type browser.newtab.url in the search box to find it on the list.
- Double-click on browser.newtab.url and type in about:newtab in the window that pops up.
Restart Firefox and open a new tab to make sure the change was made. If there is any issues with plugins please also see: Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems
Please post back with your results, we are happy to help.