Weird HTML Popup, with Join Wifi as label

[monolithic]

Since today morning I've been getting a weird popup with HTML text. The window has the Label "Join Wifi(Network Name)"

I have not installed anything and this is recurring. How do I stop this. This is becoming annoying!

 

[Deep_Thought]

I've got a temporary fix from Apple - https://forums.macrumors.com/threads/html-test-success-pop-up-in-safari.1900769/