Try this method to regain your bookmarks. First, you’ll need to show hidden files and folders. From My Computer go to Tools, select Folder options, then View, Advanced Settings, then choose Hidden Files and Folders and tick ‘Show hidden files and folders’. Then click OK. Now open Firefox and click on the Bookmarks menu, then select Organise Bookmarks. In the Window that opens, go to the File tabl and select Import. In the next box choose ‘From File’.
Navigate to My Computer, then go to C: drive, Documents and Settings, Your username, then Application Data, then Mozilla, Firefox, Profiles, then xxxx.default (where xxxx is a seemingly random sequence of numbers). Next select Bookmark Backups, select a date and choose Open. This should hopefuly show your missing bookmarks. It’s also wise to change back the hidden files setting when you’ve finished.(I took this article from another site.)