I had used a bookmark to open the chase website but it opened in a sidebar. It doesn't have an X to close it. And now when I launch Firefox it has the chase sidebar up. I tried to do what the one article I found that matched my problem. But the two suggestions didn't work for me. I did the undoing of the launch in sidebar under the bookmarks and even removed the bookmark but it still didn't work. I have tried the alt and f10 but nothing came up for me to do anything with. It is very annoying to have a sliver of a sidebar that can't close up.