Browser based Tech Support Scammers keep coming up with new and innovative methods to prevent users from closing their browsers. In this scam, when you move your mouse cursor over the web browser showing the scam, the mouse cursor disappears. Instead you will see a mouse cursor moving randomly over the page, which is the scammers trying to trick you into thinking your mouse is not working properly. Fortunately, no matter what tricks a browser tech support scammer throws at us, there is always a simple weakness. If the browser is closed, the alert goes away with it.
Source: https://www.bleepingcomputer.com/news/security/tech-support-scams-use-new-tricks-to-hold-browsers-hostage/