About a week ago, my Firefox browser started being extremely slow to load. It loaded the shortcuts but the page full of news things to click on never loaded. Instead, the rectangles where they would go were just illuminated from left to right with a gray sweep light to dark over and over. I left it going and hours later it was still doing it. I clicked on some of the shortcuts and some came up and others did not, at least during the time I was willing to wait. I went to Google Chrome and it was slower than usual but eventually I was able to get to my email, ebay, etc. I spent hours on the phone with Xfinity/Comcast and they ran tests and said everything was ok. I checked and found that I have the latest version of Firefox. Is it possible that an update caused this? If not, what is going on?