Retrieving old Bookmarks
My old laptop has died but the C: drive is fine and fully intact. If I put the old C: drive into a USB caddy, can I get the bookmarks off it to put on to my new laptop ?
Opaite Mbohovái (3)
Yes. All you have to do is find the profile folders, and then the profile you were using.
https://support.mozilla.org/en-US/kb/how-run-firefox-when-profile-missing-inaccessible
http://kb.mozillazine.org/Profile_folder_-_Firefox#Navigating_to_the_profile_folder
https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles
https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles
Once you find that profile, look for the places.sqlite file. It contains your History and Bookmarks.
You can also recover the other data as well.
Most likely, yes. Firefox stores your data under a hidden folder, so set Windows to show hidden files and folders:
https://support.microsoft.com/en-us/help/14201/windows-show-hidden-files
Then, if we assume your USB drive will be assigned drive E, then try:
E:\Users\your-user-name\AppData\Roaming\Mozilla\Firefox\Profiles
The articles in the first reply above will help you identify valuable files there.