I suggest two initial levels of clean-out, and then two settings to repair: '''(1) Extension Cleanup''' You can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. Either: * Command+Shift+a (Windows: Ctrl+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. Then cast a critical eye over the list on the right side. 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). '''(2) Malware Sweep''' A well-regarded tool for this is: https://www.malwarebytes.com/mac/ '''(3) Restore preferred home page''' This is the page that appears at startup and in new windows (Command+n). See: [[How to set the home page]]. '''(4) Restore preferred search provider''' If searches give results on the wrong site, here's how to update that setting: [[Change your default search settings in Firefox]]. Back to normal?

Thanks for your helpful suggestions jscher2000. It worked.