Hi, You can right-click and '''Toggle''' the key '''browser.newtabpage.enabled''' to '''true''', and also '''Modify''' the key '''browser.newtab.url''' to '''about:newtab''' in [http://kb.mozillazine.org/About:config about:config], if the key values are different. You may also have to make sure that the '''Home Page''' is set to '''about:newtab''' in Firefox '''Tools''' ('''Alt''' + '''T''') > '''Options''' > [https://support.mozilla.org/en-US/kb/Options%20window%20-%20General%20panel?as=u General]. # In the [[Location bar autocomplete|Location bar]], type '''about:config''' and press '''Enter'''. The about:config "''This might void your warranty!''" warning page may appear. # Click '''I'll be careful, I promise!''', to continue to the about:config page. [http://kb.mozillazine.org/About:config_entries about:config Entries] The [https://services.addons.mozilla.org/en-US/firefox/discovery/addon/config-descriptions/ Config Descriptions] add-on adds helpful source comments in about:config. If problems persist, you can reset Firefox and set the [https://support.mozilla.org/en-US/kb/How%20to%20set%20the%20home%20page Home Page] to about:newtab. The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information. Note: ''This will cause you to lose any Extensions, Open websites, and some Preferences.'' To Reset Firefox do the following: #Go to Firefox > Help > Troubleshooting Information. #Click the "Reset Firefox" button. #Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish. #Firefox will open with all factory defaults applied. Further information can be found in the [[Reset Firefox – easily fix most problems]] article. Did this fix your problems? Please report back to us! If you would like to take a listing of the add-ons, changed preferences/settings etc. to quickly replicate the previous profile, please '''Copy all to clipboard''' (on the left of the reset button), and paste it into MS Office Excel, or OpenOffice/LibreOffice Calc, or notepad. However, it would be a good idea to check for the existence of the issue immediately after the reset.

Thanks for answer I got reset. And my issue was resolved. But I do not want to reset all configuration, is there any other way?

Yes, you can start the [https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles Profile Manager Profile Manager], '''Create Profile''' > .'''Next''' > '''Choose Folder''', browse and select '''Old Firefox Data''' on the desktop and start Firefox in that. [https://support.mozilla.org/en-US/kb/Profiles?s=profile&r=2&e=sph&as=s Profiles Howto] [http://kb.mozillazine.org/Profile_folder_-_Firefox Firefox Profile Folder & Files] [http://kb.mozillazine.org/Profile_folder Firefox Profile Folder]