Firefox Homepage keeps resetting to Bing

I've read several threads here about the homepage resetting to Bing and I've tried all the recommendations. My homepage continues to reset to Bing.
I've scanned for virus' & malware w/ Malwarebytes & Defender. Also used McAfee Stinger. No problems found.
Is there a setting inside Windows 10 that prohibits the homepage from being changed?
Any suggestions are appreciated.

Update: I discovered why this is happening. I recently installed AdvancedSystemCare v9. It has a variable, buried deep down inside, where it keeps the browser homepage. Somehow during the installation, this variable got set to Bing, instead of the homepage I wanted.
I consider this solved.

Thanks for the update regarding AdvancedSystemCare v9.