You can't. The bookmarks.html format doesn't contain the Tag data. You need the JSON bookmarks backup format to have the Tag data, but restoring that file format overwrites any existing bookmarks you may have saved. Also, the JSON format doesn't currently have the Favicon (website image) data as the Firefox bookmarks.html format does.

That's really too bad. I do have a JSON file ready to import, but both options seem only half of a whole good solutions.

How about about syncing my current PC with my former PC via a USB direct connection?

Sorry, Sync doesn't work that way. You need to have the Mozilla Sync server in the middle of the "transaction", or a local Sync server which you set up.

Please explain exactly what you are wanting to do, or want to accomplish.

I have an older PC (Windows XP) running Firefox. I have a new PC (Windows 7) now running Firefox (13.0.1). I want to move all the Firefox bookmarks from the older PC and inject them into the Firefox on the new PC. I want them to go into the appropriate bookmark sections (Toolbar, Menu, Unsorted) with all the tags and icons preserved. That's what I want to do.

Firefox Sync will get all your Firefox personal data transferred from the old PC to the new PC.

See this:
https://support.mozilla.com/en-US/kb/what-firefox-sync

Set up Sync on the older PC which has the data that you want to transfer to the new PC.
https://support.mozilla.org/en-US/kb/how-do-i-set-up-firefox-sync

Then add the new PC as an additional device.
https://support.mozilla.org/en-US/kb/add-a-device-to-firefox-sync

That sounds straightforward enough. Thanks for the help.