Due to some glitches you may find sometime the bookmarks stored in Firefox become corrupted or by any reason you lost your bookmarks within couple of days, you need not to worry as you can restore them from the set of backups that Firefox maintains. Here below are steps to restore your bookmarks backups;

*  Select File from the menu at the top of the Firefox window and then select the Exit menu item.
* Reboot your computer.
* When the computer restarts, select the Start Menu in the Windows Taskbar and select Run.
* In the Run dialog, enter the following:
%APPDATA%\Mozilla\Firefox\Profiles
* Click OK.
* A window displays all your Firefox profiles as a set of folders.
* Each Profile folder is named something like the following:
xxxxxxxx.<ProfileName>
where xxxxxxxx is an assortment of random letters or numerals
<ProfileName> corresponds to the name of the profile.
* For example, the folder containing the default profile is named xxxxxxxx.default.
* Select the folder for your current profile.
* In the profile folder, the file bookmarks.html stores your bookmarks and has become corrupted. Right-click this file, and select Rename….
* Rename the file to a unique name, such as the following:
bookmarks_backup.html
* Open the folder named bookmarkbackups.
* In the bookmarks backup folder, you should see up to five files with names like the following
bookmarks-xxxx-xx-xx.html
The xxxx-xx-xx corresponds to the date the backup was made.
* You must copy one of these backups to the profile folder. Right-click the most recently dated backup. Select Copy.
* Go back to the previous folder, which now contains the bookmarks_backup.html file.
* Right-click in the white space of the folder. Select Paste.
* Right click the file you just pasted (bookmarks-xxxx-xx-xx.html). Select Rename….
* Rename the file to bookmarks.html
* Restart Firefox. now you can locate your bookmarks from the bookmark Menu.