I have been using cs50 ide for more than a year and for the first time today, for no reason I cant find the preview option for html files I dont know why this happened, it was there a few weeks ago, but all of a sudden it's not there. I tried going to preferences < user settings < preview but doesn't work. Please help!
I actually had the same issue. What you can do is right-click the file name in the directory on the left-hand side and click on "Download". Then it will download the file, you can click on it at the bottom of your browser window and it will be opened in your browser and you can preview it. Hope this helps.