I have not heard of any kind of blocking for bookmarks. Try to open the file with a file viewer. Go thru it. Does it look okay?

FredMcD said

I have not heard of any kind of blocking for bookmarks. Try to open the file with a file viewer. Go thru it. Does it look okay?

Everything looks OK. I was able to import all of them in IE with no issue.

I have also just imorted the same bookmarks html into Google Chrome, and again - no issue. Is there some sort of hidden setting within Firefox?

There is no built-in or hidden setting that is userset or one that can be tweaked by the user.

1. Was that bookmarks.html file exported from Firefox? Or another browser?
2. Did you edit that file after exporting it, and before importing it?
3. How deep do the nested folders in that Adult folder go? i.e. - folders within folders, within folders, and so on - How many levels of nesting?
4. Estimate of how many bookmarks in that Adult folder? And how many bookmarks overall in that bookmarks.html file?

If you would open that bookmarks.html in Firefox [or any browser, for that matter] you can use this bookmarklet to give you a count of the number of bookmarks in that file overall.

javascript:(function(){var%20a=document.getElementsByTagName('a');alert('Bookmarks:%20'+a.length);})(); 

You can check for problems with the places.sqlite database file in the Firefox profile folder.

• http://kb.mozillazine.org/Bookmarks_history_and_toolbar_buttons_not_working_-_Firefox
• https://support.mozilla.org/kb/Bookmarks+not+saved#w_fix-the-bookmarks-file

• Places Maintenance: https://addons.mozilla.org/firefox/addon/places-maintenance/

Boot the computer in Windows Safe mode with network support (press F8 on the boot screen) as a test to see if that helps.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/

Do a malware check with several malware scanning programs on the Windows computer. Please scan with all programs because each program detects different malware. All these programs have free versions.

Make sure that you update each program to get the latest version of their databases before doing a scan.

• Malwarebytes' Anti-Malware:
  http://www.malwarebytes.org/mbam.php
• AdwCleaner:
  http://www.bleepingcomputer.com/download/adwcleaner/
  http://www.softpedia.com/get/Antivirus/Removal-Tools/AdwCleaner.shtml
• SuperAntispyware:
  http://www.superantispyware.com/
• Microsoft Safety Scanner:
  http://www.microsoft.com/security/scanner/en-us/default.aspx
• Windows Defender:
  http://windows.microsoft.com/en-us/windows/using-defender
• Spybot Search & Destroy:
  http://www.safer-networking.org/en/index.html
• Kasperky Free Security Scan:
  http://www.kaspersky.com/security-scan

You can also do a check for a rootkit infection with TDSSKiller.

• Anti-rootkit utility TDSSKiller:
  http://support.kaspersky.com/5350?el=88446

See also:

• "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked
• https://support.mozilla.org/kb/troubleshoot-firefox-issues-caused-malware

Open the file with the proper edit program. Look for the section that can't load. Copy <Control> C Everything for that section. What about everything after that section, did it load properly?

Now, create a new, blank, html file, and paste into it. Save the new file. Now see if you have the same problem.

If the problem is the folder nesting, as the-edmeister suggested, you can edit the new file to reduce the nesting, while keeping the original file untouched.