UI and font blurry after opening HTML5 video

[Xiontu]

I encountered a problem with vivaldi after I decided to use it as my main browser. Everything was fine till I opened my usual sites. After that the UI and all fonts on the sites where blurry and fragmented. I discovered after some trial and error. That everything loaded fine till I opened a Youtube video in HTML5. After using an extension to force the Youtube player to flash and reopening the browser, everything was fine again. I can replicate it at will. So HTML5 screws somehow with the whole browser. Does someone know how to fix that?