hello, this sounds like a problem possibly caused by malware 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

You got a hijacker, and by the looks, adware as well. This malware might be installed in control panel as well, so first look through control panel entries and get rid of everything you do not need. At least conduit plugin needs to be removed from firefox plugins too. If scan with adwcleaner fails, you should Reset Firefox preferences to troubleshoot and fix problems. There are some other anti-malware programs that might help with dealply, e.g. Spybot, Spyhunter.