Your website is affected by a malware. I hope you don't use any browser based wallets because then you are at risk of loosing money. But there's an easy way to remove this malware.
Just download Emsisoft malware protection tool which comes with a free trial period. Scan you pc and remove this malware. That should solve this issue!
Nope, this isn't a malware at all. Take note that all of the browsers do take a high capacity on a user's RAM and running an auto-bet in a browser would simply make the browser run more as the user would open more applications other than that. Try using auto-bet in Google Chrome as well if your RAM is just 8gb or less. Soon, you'll see that your device would heat up as it tries to be at its maximum performance to run in background your auto-bet.
@OP, maybe you can tell us anything about your device's specs? Such as your CPU, RAM, and VCard. Because based on my understanding, running an auto-bet on a background esp in a browser would eat huge capacity in your processing units.