In the portable version I opened up the Bookmarks Library, Bookmarks > Organize Bookmarks..., then select Import and Backup > Import HTML, choose the From an HTML file option and pointed it to the bookmarks.html file. Turned off PApps and then on again. My new bookmarks in my laptop don't appear in the PortApps bookmarks bar. Only the old are still there.
You are looking at the "Bookmarks Toolbar", expecting to see the imported bookmarks.
When you import the bookmarks, they end up getting filed under "Bookmarks Menu" and not under "Bookmarks Toolbar".
Reopen Organize Bookmarks, locate the folders you want, and move them up to the "Bookmarks Toolbar" category. Then you'll see them in the Bookmarks Toolbar.
Jim
neutron1132 (at) usa (dot) com
If you're trying to import from another copy of FF3, you'll notice that bookmarks.html is no longer used. You need to export your bookmarks from another copy of FF3 to a bookmarks.html file and then import that into FFP3.
Sometimes, the impossible can become possible, if you're awesome!