Sync data transfer is one way -- to the iPhone. If you were using Sync, your data should have been recovered after the OS re-installation from the Sync server.
How do you setup Sync again on that PC, as a "new device"?
Did you have your Sync account username, password, and your Sync Key?

If Safari is capable of exporting your bookmarks in HTML format on the iPhone, do that, and then import that file into Firefox.
https://support.mozilla.org/en-US/kb/Importing%20Bookmarks%20from%20an%20HTML%20File

I feared that... was hoping for some sort of work around, even if it was tedious. As far as Safari, there are no bookmarks short of the default ones, definitely not the ones from Firefox. I do have the account name, password and sync key and that is how I set it up FF on the PC --clicking 'I have an account' and filling in the blanks. When I tried to re-pair the phone and PC, I had to do it manually (using the above information) because the 'keys' that were provided would not work.

A-ha! It is possible; I've been playing with this all day on the PC and the phone, finally progress:

I uninstalled FF and wiped everything, then reinstalled. Went to set up sync on the computer, set the options to "replace everything on computer with data on other device" and then signed in using my account, password and recovery key. All has been restored to the PC.

Again, after the (re)install of FF, even after signing in using the other two options (merge the data, etc), FF never recovered my bookmarks and data from the Sync account. ???