If it the older one is newer than 3.0.2 it use places.sqlite file and you can use a backup from the bookmarkbackups folder there to restore on you current Firefox if a complete replacement is what you want.

Otherwise, export from the older one, and import into the new one. The imported bookmarks will be added to the end of the "Bookmarks Menu" and you will have to move things where you want them and then remove the rest of the additions if unwanted.

More information

• Backing up and restoring bookmarks - Firefox - MozillaZine Knowledge Base
  Backing up and restoring bookmarks - Firefox - MozillaZine Knowledge Base
• Import bookmarks - MozillaZine Knowledge Base
  Import bookmarks - MozillaZine Knowledge Base

I still don't understand how to do this. I have a Firefox 4.0.1 on an old computer that has many bookmarks in it. i want to transfer them to a new computer that also has Firefox 4.0.1 on it. the two computers are on the my home network.

I tried to create a HTML file from the bookmarks on the old computer, but I only got a list of about 25 or 30 of the bookmarks. So I didn't actually try to save(create) the actual file since so few of the bookmarks were showing up. I am very frustrated by this.

You can export bookmarks as HTML from the bookmarks window. It is called "Show All Bookmarks" now. The last button on the toolbar in the window is the one you use, and choose Export. You can then save the bookmarks as HTML to wherever you like. With the new computer, use the same toolbar button and choose Import, and import the HTML file.

Between two 4.0.1 systems you can do almost anything in the form of complete replacement, such as replacing your entire profile with the old one. You can find your current profile by using about:support > "Open Containing Folder" do that on both computers.

aboutsupport is what you get via Help > Troubleshooting Information... then you simply click on "Open Containing Folder".

• Transferring data to a new profile - Firefox - MozillaZine Knowledge Base
  http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox
• Transferring data to a new profile - MozillaZine Knowledge Base
  http://kb.mozillazine.org/Migrating_settings_to_a_new_profile

Windows systems have hidden files and may have read only files, check out http://dmcritchie.mvps.org/windows-7/win7.htm