https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware

You can check the target line in the Firefox desktop shortcut (right-click: Properties) to make sure that nothing is appended after the path to the Firefox program.

Download the Mozilla Search Reset {web link} This add-on is very simple: on installation, it backs up and then resets your search preferences and home page to their default values, and then uninstalls itself. This affects the search bar, URL bar searches, and the home page.

Looks like a well known adware / malware "virus" based upon this Google search.

I don't see my favorite "malware tips" web site listed on the first page, so I don't want to recommend a specific page. Pick one to learn how to get rid of that pest.

My advice is to fix or get rid of the "source", as it may affect more than your Homepage in Firefox.