Since today, webpages I visit, sometimes turn blank. e.g I was watching Youtube video. I switched to another tab and than back to video and the page was blank. I could not see anything. However, the video was still playing. Even when I click on a place where video is suppose to be the video stops. If I click again, video starts. Youtube behave like it should, but I cannot see anything. I tried to refresh the page but it does not help. what helps is to close tab and open new one. or restart firefox. This is happening on multiple webpages. I would say on most of webpages I visited today.