Make sure you've signed in to your Firefox browser both on your PC and phone with the same account and have turned on the sync. Also do check if the version of Firefox installed on both the devices is latest.

You can manage your firefox account here: https://accounts.firefox.com/

Thank you very much, Ramansgdeep! In the meantime I myself have solved the problem of Firefox no longer being accessible on my computer by downloading a new version of Firefox. I thought I would have had to reinstall my old bookmarks (which I had saved to the desktop) but they were already there in the new downloaded version of Firefox (how did it know ;). I have had second thoughts about letting all of my bookmarks, history and downloads be present on my relatively unprotected iPhone - in terms of malignant attacks (and what if it gets stolen!) - and therefore have since removed Firefox from my iPhone.

Hello,

I am glad to hear that your problem has been resolved. If you haven't already, please select the answer that solves the problem. This will help other users with similar problems find the solution more easily.

Thank you for contacting Mozilla Support.

Firefox comes in two or more folders on all computers. They are;

Maintenance: (Programs Folder) <Windows Only> Firefox itself: (Programs Folder) And two folders in the profile of each user on the computer for each Firefox profile for that user.

If you remove the Firefox folder, the user profiles would not be affected.

Thanks, Fred McD!

You are welcome.