hello, this sounds like a problem possibly caused by adware on your pc. please go to firefox > addons > extensions & remove any suspicious entries (toolbars, things that you have not installed intentionally, don't know what purpose they serve, etc). also go to the windows control panel / programs and remove all toolbars or potentially unwanted software from there and run a full scan of your system with the security software that you have in place and different other tools like the free version of malwarebytes & adwcleaner.

Remove a toolbar that has taken over your Firefox search or home page Troubleshoot Firefox issues caused by malware

thanks, disabling a bunch of plugins I didn't need seems to have fixed it.

I found "Search Assistant MocaFlix 1.66" in my Program list.

Avast AntiVirus, Spybot Search and Destroy, and Anti MalwareBytes did NOT detect this malware (at least on the day that I wrote this).

What is Search Assistant MocaFlix? Search Assistant MocaFlix is a web browser extension that is designed to deliver ads. It is considered adware and modifies the user's web browser settings including the default home page and search settings. It also installs the SProtector plugin which prevents other applications from modifying the changed browser settings. Websearch.mocaflix will constantly redirect your internet connection and tell you that you are browsing unsafely. Overview Search Assistant MocaFlix 1.66 is a software program developed by Search Assistant SProtector. The primary executable is named sprotector.dll. A majority of users end up uninstalling this less than a week of it being installed. The setup package generally installs about 2 files and is usually about 802.46 KB (821,716 bytes). Relative to the overall usage of users who have this installed on their PCs, most are running Windows 7 (SP1) and Windows 7. While about 15% of users of Search Assistant MocaFlix come from Taiwan, it is also popular in the United States and Ireland.