I have seen some similar things to this. Oddly enough, in every case it has been in Chrome (on PC and my phone). Matter of fact, one of these things is the reason my mother in-law actually called the number...lol Here's my post on that ordeal https://www.technibble.com/forums/threads/what-the.70303/#post-552571
Numerous times I have run into this and especially with Chrome. Clear out the extensions and revert to default settings on Chrome. Would also throw JRT and Adwcleaner at it.
I have run adwcleaner as well and it came up as clean. The extension are are disabled. No recent program installed. In the past it has been more ie than chrome
Have you tried ORT: www.oakslabs.com ? I take a more aggressive approach to cleaning the browsers. Also, make sure this is not set to the home page (that's a bad setting, and most AV/AM programs don't check those....)