I assume this problem is on a Windows PC and not on your Android device?

Please use the cleaning tools in this support article: Troubleshoot Firefox issues caused by malware. In particular, AdwCleaner and Malwarebytes Anti-Malware (free edition) should help.

Then, to reset your Firefox home page, new tab, and search engine settings back to their defaults, you can use this extension: https://addons.mozilla.org/firefox/addon/searchreset/

I also recommend going to the Windows Control Panel. Depending on your version of Windows, it's either:

• Uninstall a Program
• Add/Remove Programs

Click the "Installed on" column heading to group the entries by date. This is helpful in uncovering bundled items that may have snuck onto your system with some free software. I suggest cleaning out everything you do not recognize as useful that was added in recent days before this problem started.