I need to know a little more about where this folder was. Was it:

• A folder of bookmarks, either on your Bookmarks Toolbar or Bookmarks Menu?
• A folder on your hard drive (e.g., inside your Downloads folder or another folder)?
• A folder on a web service such as Dropbox or Skydrive?
• Some other folder?

By the way, if you're looking for downloads, try this: open the Downloads list (Ctrl+j), right-click the entry and choose Open Containing Folder.

The lost folder was a sub-folder to a main folder in my bookmarks sidebar on my main hard drive I could search for urls in the sub-folder and find them, so they still exist . I suspect the sub-folder was accidentally moved under another folder. BTW, isn't there an addon or extension that expands the "open containing folder" function to other areas. Thanks for your support.

Can you remember any of the sites in that folder? If so, you could try the following:

• Search for the site using the search box at the top of the bookmarks sidebar and follow the bookmark.
• Click the yellow star in the URL bar, and the current folder name will be shown on the drop-down in the middle of the dialog. Click the button at the far end of that line (downward-pointing caret) and pull the scrollbar down until you see the folder highlighted.

If that method doesn't work, you could export your bookmarks to an HTML file and view it as a webpage. Actually, this might be a more useful method because you could keep the page open while organizing your bookmarks. This article has the steps: Export Firefox bookmarks to an HTML file to back up or transfer bookmarks.

Any luck?

Edit: After posting, I see you were able to find them in a search, but I'll leave the first line for future reference by others.

Try to open the bookmarks in the sidebar (Ctrl+B) and click in the bookmark area to set focus to that area and then quickly press the first letters of the lost folder to see if that brings up that lost folder.
The search bar only searches bookmarks and not folders and doesn't show the location of bookmarks that are found.
You need to click at the far left in that area to prevent opening the bookmark.