Please use this link- https://www.mozilla.org/en-US/firefox/new/

Sounds that the history got cleared. unfortunately Firefox doesn't keep a backup of the history.

Firefox manages downloads in the Downloads folder in the Library (History > Show All History)

• Downloads are treated as history items: clearing history removes included download items and vice versa.
• The Download button gets a blue highlight once all downloads are finished to make you aware that new downloads are available.
• Pause and Resume can be found in the right-click context menu of an item.

You can check in Windows Explorer if there is a previous version of the places.sqlite file available.

• Right-click: Properties > Previous Versions
• http://windows.microsoft.com/en-US/windows7/Previous-versions-of-files-frequently-asked-questions

Note that places.sqlite stores bookmarks and history, so if you need to keep recent bookmarks then make sure to make an HTML backup of the bookmarks.

• https://support.mozilla.org/kb/restore-bookmarks-from-backup-or-move-them

It answered my question concerning why the downloads disappeared but raises another. I have chosen different folder, also named downloads, on a different drive as the location for downloads. Will that prevent Firefox from treating them as history?

There is a downloads folder on my C drive and all of my previous Downloads are still there, so apparently Firefox does not see them.

Thank you for the help, I am very new to Firefox.

No, all downloads are basically history items like when you visit a website and the download location is the history item. It doesn't matter to what folder you saved the file.

The files should still be in the location where you saved them unless you removed them, only you can no longer access them via the download history.