see this answer:

• https://support.mozilla.org/en-US/questions/1124007#answer-879695

My old computer is completely broken, it wont even start in safe mode. And my hard drive is an old HDD so I can't install it in my new computer. I'm using a USB Hard Driver Adapter to connect the old HDD to my new computer to gain access to it. When I try to open the version of Firefox on my old HDD it wont open because it is not compatible with Windows 10 so I can't do the usual export/import HTML file for my Bookmarks. What I need is a work around for this.

Are you able to access the Firefox profile folder on that older drive?

You likely need to enable hidden files.

Location used for the main profile that keeps your personal data in "AppData\Roaming".

• C:\Users\<user>\AppData\Roaming\Mozilla\Firefox\Profiles\<profile>\

"AppData" is a hidden folder.

• http://kb.mozillazine.org/Show_hidden_files_and_folders

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

See also:

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

Thank you! I copied the "places.sqlite" file from my old profile into my new one and it did the trick.