Hi. My name is***** you for your question and the opportunity to assist.
You can give Firefox a tuneup and this should correct things. Click the 3-bar icon in the upper right corner
and click the ? icon at the bottom and select Troubleshooting Information.
Click Refresh Firefox twice and the refresh will run.
When Firefox reopens you'll need to re-enter your home page information.
Click the 3-bar icon and select Option and set your home page up there.
Let me know the result please.
It's also possible this is coming from some type of malware infection.
Possibly from Mindspark.