This problem has just started over the past week. When I need download a pdf file (such as tickets etc) it shows as 'Unknown size' so I cannot open it. The dowload list shows only downloads done months ago - although, up to last week, I had no problem. Cory MH replied earlier this week suggesting the following but I am not sure how to access the information. This is screen shot of the advice: Can you check the properties of your places.sqlite file, which handles your bookmarks, browsing history, and downloads? It is contained in your Firefox profile folder, which you can access by going to the about:support page or: • Help (or > ) > Troubleshooting Information On that page, click the "Show Folder" button and that will open your profile folder in Windows Explorer. Look for the places.sqlite file and right click it. Select Properties and under the General tab, make sure that it isn't "Read-only". You can also install the Places Maintenance extension to run maintenance on the file to see if that can fix it if it is corrupted. Please read the following articles first as they provide helpful hints and instructions that may be relevant to you: I really need clarification as to where to find the 'about:support page' on Help/Troubleshooting etc. This problem is a real nuisance as I will need to dowload boarding passes later in the week. Thanks for any help Rosie