Hey there!

Seems like some suspicious activity has happened!

See:

https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware

As co-rel said

"You can check for recently installed suspicious or unknown extensions.

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

   switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Themes
   do NOT click the "Refresh Firefox" button on the Safe Mode start window "

Hope I helped!

Kind regards,

Bithiah

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. Make sure you know what each one is and what it does.

Hey there!

If your problem is solved, please mark a solution so that others can see this thread is solved. Thank you in advance!

Kind regards,

Bithiah