I just clicked at a link that's is linking to a txt file. Firefox nicely showed the txt file in the browser. But! All history is gone. It's not possible to go back. Complete Firefox is blocked. If I click at the + sign to add another TAB it's not showing the tab. When I close Firefox it warns me I have several tabs open. But I can only see the one with the txt file! So when I clicked the + FF did open a new tab only it's not shown anymore. I have to shutdown FF completely and restart it to be able to use it again.