Is Google your default search engine?

If not; Type about:addons<enter> in the address bar to open your Add-ons Manager. Hot key; <Control> (Mac=<Command>) <Shift> A)

In the Add-ons Manager, on the left, select Extensions. Remove “ Google “ Anything. Also look for SafeSearch or SearchAssist Incognito.

Now do the same in the computer’s Programs Folder.

Windows: Start > Control Panel > Uninstall Programs. Mac: Open the Applications folder. Linux: Check your user manual.

Google lead services is a fake security program which is designed by hackers to rip off gullible computer users. Google lead services can invade your computer very easily and won't let you run any programs. Everytime you turn on your computer it scans your system automatically.

After you have done as FredMcD adviced you to do :

As most malware will be 'hiding' somewhere, let's run some malware scans :

Further information can be found in this article :
https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware?cache=no

Run most or all of the listed malware scanners.
They all work differently   -   what one program doesn't pick up, the other might.