If you have bookmarked lots of websites, you might have a few duplicates in your bookmark bar. A good way to clear up your bookmark bar is to remove duplicated page links, and you can do that quickly with the Bookmark Duplicate Cleaner add-on for Firefox and AM-Deadlink software.
This is the Bookmark Duplicate Cleaner page  on the Mozilla add-on website. Open that page, click on + Add to Firefox, Install Now and restart the browser. Then click Tools on the menu bar and select Bookmark Duplicate Cleaner to open the window below. If the menu bar isn’t at the top of the browser, select Open menu > Customize > Show / Hide Toolbars and then select Menu bar.
The page will display any duplicate bookmarks. Click on the bookmark titles to open links to their pages on the right of the window. Select one of the locations on the right and click on Open to open the page.
To delete bookmarks, you should select the locations on the right of the window. Hold the Ctrl key to select multiple locations. Then click on the Delete button to remove the duplicate bookmarks from the window.
Of course, those with alternative browsers to Firefox will not find the Bookmark Duplicate Cleaner add-on much use. To delete Chrome, Opera and Internet Explorer duplicate bookmarks, consider adding AM-Deadlink to Windows from this page . AM-Deadlink is a freeware package that detects dead links and duplicate bookmarks.
Once you have opened the window above, select a browser from the drop-down window. That will show you a list of the browser’s bookmarks. Then select Bookmarks > Find Duplicates to filter out duplicated links as below. Click the Delete button to remove them.
So with Bookmark Duplicate Cleaner  and the AM-Deadlink package  you can quickly find and delete duplicated bookmarks. For further details, check out the Bookmark Duplicate Cleaner and AM-Deadlink homepages.