After clicking on a link yesterday the screen shown below appeared. I am not able to delete it. This happened to me a few months ago, I think on the 21st August - at least I have found a copy of sessionstore-backups folder with that date in My Documents. As I keep a large number of open tabs I wanted to preserve these. Back then I located the sessionstore.js file, opened it in the editor notepad++, searched for the web address of the faulty tab, and deleted a few characters in it. When I restarted Firefox that tab now reported Page not Found, and I was able to delete it. So, this time I was going to do the same thing. Except that the sessionstore.js in the profile location is not the current one. It is dated 28/09/2017, and is present when Firefox is running - which I gather it shouldn't be. In the sessionstore-backups both the previous.js and recovery.js are also dated 28/09/2017. There are three files in sessionstore-backups with today's date, these are: recovery.jsonlz4 recovery.baklz4 previous.jsonlz4 Can these files be used somehow to get at the currect sessionstore.js? I would be grateful for any advice. Incidentally, I am running Windows 7 Professional, and I keep it fully updated. I use the Microsoft Windows Defender and Panda anti-virus. The link I clicked on which caused the problem was about some Photoshop techniques I was interested in. I regard myself as a safe browser - I don't go nosing around the more dodgy areas of the net where you might expect these things. I have lost no files or data the first time or this time. I didn't realise it at the time, but the log on box displayed is for my router, so I guess it is blocking the attack somehow.