Firstly, startup the 'Run' command (Start button --> Run). Type "%APPDATA%\Mozilla\Firefox" into the box and click "OK" (as shown in Figure 1).
Figure 1
If no error occurs, a folder will open as shown in Figure 2.
Figure 2
Proceed by opening the "Profiles" folder until you've entered a folder named "bookmarkbackups" (as shown in Figure 3). Here is where your previous 5 days backup of bookmark is stored.
Figure 3
Each file is named as such "bookmarks-(backup-date)". Start by opening the latest date available and check if that file is working. A corrupted file may be empty, or may contain non-alphanumeric characters. If the file is corrupted, try the next latest date, until you found one that is working. A working file will list all your previous bookmarks accordingly.
Once you've found a working backup file, you may restore your bookmarks using one of the following 2 options below:
1. In Firefox, open the Bookmarks Manager (Bookmarks --> Organize Bookmarks...). Open the following menu (File --> Import). Select the "From File" option and click "Next". Select the working backup file, and proceed.
2. Note: All current bookmarks will be lost. Choose option 1 if you've any bookmarks you would like to keep.
Close all Firefox browser. Rename the backup file to "bookmarks.html". Next, copy and overwrite the backup file to the parent directory which contains another "bookmarks.html" file (which is your current bookmark).
Eg: Copy and overwrite "bookmarks.html" from "...\Profiles\by8e3pfj.default\bookmarkbackups" to "...\Profiles\by8e3pfj.default".
If you're using a different operating system from Windows XP, click here to find out where your backup bookmarks folder is located.
For more information, read this.
There you have it. Hope this tutorial helps.