"I have had a notice pop up about once a minute saying that Su2.ff.avast.com is malicious and is being blocked. I've run Malwarebytes and found nothing."
su2.ff.avast.com has been reported to bother lots of computer users in a recent period of time. This ad-supported thing, distributed by a third party, sneaks in users' systems and then take a hand in their computer activities regardless. Needless to say, su2.ff.avast.com, acting like a redirect virus, is good at taking control of browsers. If you are one of the sufferers of this culprit, you could be driven nuts by its perpetration.