I do not use a Mac. But when you install a new version of Firefox it will try to use existing settings etc from what is known as the profile. The profile includes your bookmarks.

• see Profiles - Where Firefox stores your bookmarks, passwords and other user data
• Recovering important data from an old profile

If you share a computer with someone normally each user has their own profile, and there may be permissions preventing users accessing one-anothers accounts. Firefox will normally setup a profile in each account. You will need to search for and find your old profile.

• Any idea where your own old profile is ?
• Have you still got the old computer, and is it in working order
  • or is your daughter's computer the only one you had?
  • who set up Firefox initially was that yourself, your daughter or someone else ?
    (They may understand how it was set up)

Did you backup your bookmarks or your profile, or sync with any other device?

My old computer is not working, which is why I was using my daughter's external drive, where I had backed up the old computer. My daughter and I have our own distinct Firefox accounts that we each set up on our own. I notice that my account on my iPad is configured correctly, and I wonder if I can transfer that profile to my new iMac.

I do not know much about Mac s

Standard Firefox probably does not work on an iPad. Syncing is between a computer and a mobile device but the static device needs setting up first with a profile that is the source of the sync.

 I was using my daughter's external drive, where I had backed up the old computer

That suggests you may have a copy of your old profile on that external drive, but you inadvertently used your daughter's. Do a full search of the external drive. Look for the file places.sqlite that will exist in each profile. You may be able to find the profile you need.

You can create a new profile.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles