Has it taken over as your home page? The home page appears every time you press Ctrl+N, so that is a quick test.

The home page can get set using the Custom URLs field or with an add-on. More info: How to set the home page. Can you regain control on the Settings page?

Cleanups

'(1) Add-ons

You can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. Either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• type or paste about:addons in the address bar and press Enter/Return

In the left column of the Add-ons page, click Extensions. On the right side, find the "Manage Your Extensions" heading.

If there is at least one extension before the next heading -- "Recommended Extensions" -- please continue:

Then cast a critical eye over the list below that heading. Any extensions Firefox installs for built-in features are hidden from this page, so everything listed here is your choice (and your responsibility) to manage. Anything suspicious or that you just do not remember installing or why? If in doubt, disable (or remove). For your privacy and security, don't let mystery programs linger here.

If your Add-ons page is blank or is blocked, you can restart Firefox in its Troubleshoot/Safe Mode to do the above review:

In Firefox's Safe/Troubleshoot Mode, Firefox temporarily deactivates extensions, hardware acceleration, any userChrome.css/userContent.css files, and some other advanced features to help you assess whether these are causing the problem.

If Firefox is running:

You can restart Firefox in Safe/Troubleshoot Mode using either:

• "3-bar" menu button > Help > Troubleshoot Mode... (before Fx88: Restart with Add-ons Disabled)
• (menu bar) Help menu > Troubleshoot Mode... (before Fx88: Restart with Add-ons Disabled)

and OK the restart. A small dialog should appear. Click the Open button (before Fx88: "Start in Safe Mode" button).

If Firefox is not running:

Hold down the Shift key when starting Firefox. (On Mac, hold down the option/alt key instead of the Shift key.) A small dialog should appear. Click the Open button (before Fx88: "Start in Safe Mode" button).

Note: Don't use the Refresh without first reviewing this article to understand what will be deleted: Refresh Firefox - reset add-ons and settings.

Any improvement?

(2) External installs

This support article can help with scanning for and removing malware: Troubleshoot Firefox issues caused by malware.

Also, if you think the add-on/malware may have connected to your Google account or Gmail as a service, go into your Google Account settings and disconnect it so it doesn't have continued access. Maybe also change your password once you are clean.