When I tried opening Firefox today something strange happened. Instead of opening up the browser, a Profile screen came up where it was asking for me to enter a profile and then I could start Firefox. There was a default one there but when I tried to select and enter that, it told me that the default one was already in use. So I created a new profile, which allowed me to enter the browser, and it seems that Firefox has started afresh.

All my extensions, themes, downloads, bookmarks and everything else that I have personalised is gone. I went to Program Files and to the Mozilla Firefox folder and saw that there were none of my extensions or themes in their respective folders.

What happened?
How can I get Firefox back to the way I had it...do I have to download everything from scratch again?

The profile, including your bookmarks etc, is still likely to be there. It just needs restoring. I could write down the steps to follow and appear to be the clever one but this chap has already done it, so I'll be lazy and let him do the explaining. Follow this procedure and see if this gets you back to normal.

It's as well to keep a recent copy of your bookmarks file (bookmarks.html) stored somewhere safe. The customizations you make to Firefox can always be re-done but if the bookmarks ever get lost, that's a real nuisance (to say the least!).

Put out a Windows search for bookmarks.html. It will find two instances of it since you created a new profile (one from each profile). Back up the one with the larger file size. This will contain your bookmarks information. You can double-click the file just to be certain. It will open up in your browser and you should be able to read the bookmarks. Take a copy of it from the seach box.