Go to Settings , then HELP, then try TURN TROUBLESHOOTING MODE ON, then look for where it says refresh FIREFOX

OR LISTEN TO THIS PREVIOUS ANSWERED QUESTION SIMILAR TO YOURS

https://support.mozilla.org/en-US/questions/1134894

or this

https://support.mozilla.org/en-US/kb/remove-toolbar-has-taken-over-your-firefox-search

Good Lucks

You can check for recently installed suspicious or unknown extensions.

Start Firefox in Troubleshoot Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration or if userChrome.css/userContent.css is causing the problem.

• switch to the Default System theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click "Refresh Firefox" in the Troubleshoot Mode start window

• https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

You can check for recently installed suspicious or unknown extensions.

No any malwere extention. The theme set by default, the "new tab" setting by default is well

Go to Settings , then HELP, then try TURN TROUBLESHOOTING MODE ON, then look for where it says refresh FIREFOX

Will i lost all by settings if refresh?

OR LISTEN TO THIS PREVIOUS ANSWERED QUESTION SIMILAR TO YOURS

https://support.mozilla.org/en-US/questions/1134894 </blockquote>

Thanks. AdwCleaner works for me too