Norton security scan is normally fine. It often comes on new PCs. Although it's likely you have a rogue version.
You can download the norton removal tool here which I think will remove it, if it's genuinely the norton version.
Regarding the search page - have you looked in the settings of firefox.
It might be a good idea to run a malware bytes scan as it sounds like it's potentially infected you
Go to free download. It gives you a full 14 day trial which is plenty to find and remove any of those nasties.