Not exactly software, but i would recommend uBlock Origin (which block ads, tracker or other stuff) no matter what browser they use.
Is an anti virus truly safe? Do they not scan computer files? If yes, does my wallet.dat file not get scanned in the process? Sure, you can add the Bitcoin folder to the list of exceptions. But still, the popular and best anti viruses are closed source. I do not trust them.
Not really, although it's likely you're in bigger risk if you don't have good security practice.